Goal of this blog is to educate and empower doctors and healthcare professionals to understand microbiology and infection. Promote understanding of micro-organisms and how they cause infection, ensure appropriate choices when prescribing antibiotics, enable best practice for infection control management and ulimately provide better patient care.
I was recently asked about antibiotics to treat a difficult infection caused by an extremely resistant Gram-negative bacterium and so I thought it was time to go back and look at what antibiotics are being developed for these situations. One antibiotic caught my eye, Cefiderocol, and I thought I ought to read more about it and see why it might be useful in the future.
What is Cefiderocol? Cefiderocol is a cephalosporin antibiotic currently in clinical trials. It is a hybrid of Ceftazidime and a siderophore side chain… but what the heck does that mean and why does this matter?
A siderophore, from the Greek for “iron carrier”, is a small molecule produced by bacteria to help them scavenge iron from their environment. Iron is essential for bacteria, they cannot survive without it, and so they have come up with mechanisms like siderophores to help them get as much iron as possible. Siderophores bind to iron molecules and these combined molecules are then detected and actively transported into the bacterial cell; it’s like the iron needs a ticket to get in and the siderophore is the ticket.
By combining an antibiotic with a siderophore the bacterium can be tricked into actively taking the antibiotic into the it’s cell, a process Microbiologists have termed a “Trojan horse” strategy (remember in Greek mythology Greek warriors hid in a wooden horse that was taken into the city of Troy as a “gift” and then the Greeks snuck out at night, opened the gates and sacked the city). The siderophore is “hiding” the antibiotic allowing it to be taken into the bacterial cell where it can damage the bacterium. This clever strategy leads to much higher intracellular antibiotic concentration than would occur without the siderophore and cunningly it bypasses mechanisms of resistance that might stop the antibiotic from entering as well… very clever!
Laboratory studies Cefiderocol is very active against Gram-negative bacteria such as the enterobacteriales (previously called the enterobacteriaceae) E. coli and Klebsiella spp. as well as Pseudomonas aeruginosa, Stenotrophomonas maltophilia and Acinetobacter baumannii including strains that showed resistance to the carbapenem antibiotics such as Meropenem and Imipenem.
It seems that the siderophore side chain also provides 10-100x more stability against breakdown by carbapenemases of Ambler classes A, B and D than for Ceftazidime without the siderophore, including those from the “big five” such as KPC, VIM, IMP, NDM and OXA. Cefiderocol is usually active (reported to be about 99%) against these bacteria but that’s not 100% and it doesn’t seem to be entirely predictable but remember no antibiotic is 100% reliable.
Recent studies have also shown potential for Cefiderocol in the treatment of AmpC producing Gram-negative bacteria. The siderophore seems to give a low affinity for AmpC enzymes as well as a low risk of inducing the production of AmpC in bacteria that have the ability, but do not always have the ability switched on, such as P. aeruginosa and Enterobacter cloacae. Over production of AmpC when combined with a loss of a porin (hole) in the cell membrane of Gram-negative bacteria can lead to carbapenem resistance so having less ability to induce AmpC and bypassing the porin as a way to get into the cell seems like a pretty good strategy for getting around this mechanism of carbapenem resistance as well.
Clinical studies In clinical studies Cefiderocol was shown to be well tolerated at doses of 2g TDS intravenously; unfortunately there is no oral version of this antibiotic but then there is no oral version of Ceftazidime on its own either. Like other Cephalosporins it is mainly eliminated by renal excretion.
There is an on-going Phase 3 clinical trial using Cefiderocol openly to treat serious infections caused by carbapenem resistant Gram-negative bacteria and another randomised and blinded study comparing against Meropenem in the treatment of hospital or ventilator associated pneumonia with Gram-negative bacteria. Many of us are waiting to see how these go and hoping that Cefiderocol will “pass” these tests with shining colours!
Tissue penetration Cefiderocol at 2g TDS IV has been shown to give good serum levels with a maximum concentration of 140mg/L. The serum half-life is about 2 hours.
Cefiderocol is 60-70% excreted unchanged via the kidneys and so has excellent levels in urine.
In studies looking at the ability of Cefiderocol to treat pneumonia it has been shown that bronchoalveolar fluid concentrations are about 10% of serum concentrations (maximum 14mg/L) with the same half-life.
Most bacterial MICs for Cefiderocol are <2mg/L so these pharmokinetic and pharmacodynamic studies show that Cefiderocol should be good at treating systemic, urinary tract and pulmonary infections.
Cefiderocol resistance Cefiderocol resistance has unfortunately already been seen in laboratory studies, especially with P. aeruginosa isolates. It is not common and so far >99% of isolates are sensitive, but it is worrying none-the-less as this antibiotic hasn’t yet been used widely and resistance already occurs. The mechanism of Cefiderocol resistance isn’t completely understood but is thought to be due to mutation in the siderophore transport mechanism (no longer accepting wooden horses as gifts!) in combination with other mechanisms that traditionally give resistance to Ceftazidime when it is used in its normal form e.g. mutation of the penicillin-binding protein to which Ceftazidime normally binds.
Cefiderocol won’t be the only answer to all of our antibiotic problems. Resistance will develop; it’s inevitable, as bacteria evolve to overcome the next challenge for their survival. In addition, Cefiderocol is only active against Gram-negative bacteria so is no use against the Gram-positives such as Staphylococcus aureus or Enterococcus spp. and let’s not mention the increasing “popularity” of beta-lactam allergy; Cefiderocol is a beta-lactam and so if you are allergic then you won’t be able to have it anyway!
Having said all of that I am still excited about the possibilities of Cefiderocol, we need more anti-Gram-negative antibiotics and this one seems to have promise. Let’s see what happens in the clinical trials…
Another word of caution Whilst I may want to get hysterical about the potential value of Cefiderocol it is important to note that all of the primary research into Cefiderocol so far has been done by Shionogi & Co. Ltd from Japan, who is the producer of Cefiderocol! Now this is the way it will be at first as it is their drug and they won’t want to disclose trade secrets but it does mean we’ll have to wait for further, more open and robust, clinical trials and experience of its use by those without potential conflicts of interest before we finally yell “hooray for Cefiderocol”… but fingers crossed this won’t be long.
Last weekend the Nuts & Bolts team (except cats!) went to the cinema to watch the new film about the early life of J.R.R Tolkien. I have been a fan of Tolkien since reading The Hobbit at the age of 5 years old and The Lord of the Rings when I was 6… okay this is early to read this book; I didn’t understand much of the dark bits but I was captured by the heroic story and have read it again many times since… the ECIC cannot understand this, she thinks it’s weird to read a book when you already know how it’s going to end… maybe she’s right, but that won’t stop me, where did I leave my copy, or my second copy or that third copy or… Surely you can’t connect Tolkien with microbiology!? Read on to find out more…
Tolkien enlisted in the Lancashire Fusiliers and was sent to the Western Front in June 1916 to join the Somme offensive. He was assigned as a Lieutenant in the signal corps and put in charge of enlisted men; there is a great quote from him, "the most improper job of any man... is bossing other men, …not one in a million is fit for it, and least of all those who seek the opportunity”… a sentiment I share.
On the 27th October 1916 Tolkien developed “trench fever” and was eventually invalided home on the 8th November. Shortly after, the battalion he left behind was virtually wiped out in the fighting; if it hadn’t been for trench fever Tolkien almost certainly wouldn’t have survived The Great War and The Hobbit and The Lord of the Rings would never have been written.
Back in 1916 there was no treatment for trench fever. Tolkien convalesced for a month in hospital in Birmingham before serving on the home front for the rest of the war. His infection relapsed many times and he was never fit for front line service again.
What is trench fever? Trench fever is the old fashioned (World War I) name for a bacterial infection caused by Bartonella quintana. The bacterium is transmitted by the bite of an infected body louse (Pediculus humanus corporis). The bacterium multiplies in the intestine of the louse throughout its life time, about 5 weeks, and is transmitted via infected louse faeces which would then invariably contaminate a scratched louse bite or other wound and enter the person’s blood stream.
The incubation period of trench fever following contamination of a bite/wound is about 7 days (range 5-20 days) and once infected bacteria circulate in the person’s blood stream ready to infect further lice when they bite, and so the cycle continues.
Soldiers in The Great War were riddled with lice; the unsanitary conditions in which they were living made this inevitable. They were bitten mercilessly and would often resort to using a candle flame to heat up the seams of their filthy uniforms in order to try and destroy as many of the louse eggs as they could… apparently they would hear a satisfying “pop” when they got one. Lice migrate from abnormally hot conditions (febrile), or abnormally cold, in search of normothermic people. They easily spread from person-to-person and trench fever, as it was called, became an epidemic problem amongst soldiers.
More than a million soldiers in The Great War had trench fever; it was so bad that the War Office set up a Trench Fever Investigation Commission to try and find first the cause and then a cure. They did discover the cause but failed to find a cure.
Nowadays, trench fever is primarily seen in situations where sanitation has broken down such as in conflicts, refugees and other humanitarian crises.
How does trench fever present? Trench fever usually presents with a fever associated with a headache, malaise, lower leg pain and dizziness. The fever often relapses every 5 days (hence the name B. quintana – from the Latin “quinque” meaning five). Splenomegaly, a macular rash and conjunctivitis can also occur.
Untreated trench fever often follows a relapsing course with further episodes occurring every few months or years.
How is trench fever diagnosed? In the past we used to do serological tests looking for antibody against B. quintana. These tests are no longer available in the UK as there are problems with cross-reactivity and false positive results. The sensitivity was about 53-65% and the specificity was 91-93%; that meant a false negative rate of 35% and a false positive rate of 7%... so not a great test.
Bartonella spp. will occasionally grow in blood culture systems, but can take 21-45 days. Prolonged incubation is essential and it is crucial that the lab is told that Bartonella spp. infection is part of the differential diagnosis so they can prolong the incubation period. UK laboratories tend not to extend incubation beyond 14 days due to lack of capacity therefore it is extremely unlikely we would ever grow B. quintana unless we “really try” to.
Nowadays PCR is the only real option for trying to diagnose trench fever (or in fact any Bartonella spp. infection). PCR can be performed on blood samples as well as tissue samples (e.g. heart valves). The main draw back to PCR is that it requires the bacterium to be circulating in the blood stream and so between relapses the test can be negative. The sensitivity of PCR on blood is about the same as serology, about 58%, and so false negatives still occur. However, PCR has a better specificity of 100% so no false positives. PCR on heart valves is much better though with a sensitivity of 95% and a specificity of 100%.
NB If you struggle with the concept of false positives and true negatives there is a new section in the book which explains all that predictive values gobbledygook!! Thanks for all those of you who have purchased a copy; the ECIC has been paid her sweet allocation from the proceeds!
How is trench fever treated? The normal treatment of trench fever is 2 weeks of IV Gentamicin PLUS PO Doxycycline, followed by a further 2 weeks of PO Doxycycline. Antibiotic treatment is only about 80% effective and relapses requiring repeated treatment (with same as above) do occur.
For endocarditis, treatment duration depends on whether the infected heart valve can be removed. If the valve is removed PO Doxycycline should be continued for 6 weeks; if surgery is impossible then the duration of PO Doxycycline is 3 months.
Careful attention should be made to killing off lice as part of the patient’s treatment as well.
Infection control There are no specific infection control measures as there is no direct person-to-person spread of infection. HOWEVER, a history of trench fever is an absolute contraindication to donating blood for transfusion as the bacterium can be spread via contaminated blood.
So was the film Tolkien any good? Well I think it should be said that the film is “based” on Tolkien’s life and is not completely accurate; but then the Peter Jackson films of The Lord of the Rings also had many inaccuracies and were only “based” on the Tolkien book and don’t get me started on The Hobbit which in some respects only really appeared to share the name! However it is an entertaining story of a period of time in which there was a lot of social change which still resonates today. If you are a fan of history and period dramas then it’s worth watching, but remember, I’m biased by being a bit of a Tolkien groupie!
Editorial note: as a non-Tolkien fan, the costumes were good and it felt “wholesome” but the film was a bit incoherent in places and lacked a strong storyline… however it did come with popcorn, and who can argue with that!
“We have a young child with a fever and a rash who isn’t very well and we want to test for measles” said the Junior Doctor working in Paediatrics.
“Have they been vaccinated?” asked the Microbiologist in reply.
“No, their Mum was worried about the vaccine and so they haven’t had it done” was the response.
“Do they have any spots in their mouth?” asked the Microbiologist.
“They don’t have any spots, it’s not Chicken Pox it’s more like measles…” replied the Doctor sounding confused.
“They’re called Koplik spots, maybe get a Consultant to have a look. Is the child isolated?”
“Errrmmmm…” replied the Doctor “I don’t think so…”
“Damn! Measles is highly infectious. Get the child isolated, look in the mouth, and I’ll arrange for a diagnostic kit. I’ll also need to start the infection control process rolling in case you have exposed anyone to measles…” the Microbiologist exclaimed.
After hanging up the Microbiologist popped his head into the infection control team’s office… ”you’re not going to be happy about this one…!” he said with a grimace on his face.
What is measles? So almost everyone these days knows that measles is a viral infection that causes a fever and a rash… or is it?
The Measles Virus is part of the Paramyxoviridae family which is part of the larger group of Morbilliviruses. In fact the rash caused by measles is called a morbilliform rash, and any rash that looks the same is given the same name; the rash is red and macular (not raised and cannot be felt) and usually 2–10 mm in diameter but may be confluent in places.
In 2018 in Europe, there were more than 82,500 cases, three times more than 2017. Measles has a mortality of 1 in 1000 cases and in 2017 there were 110,000 deaths Worldwide. The myth that measles is a trivial febrile rash illness is wrong; measles can kill. Any death from measles is a tragedy since measles is a preventable disease.
So far in the UK this year there have been over 800 cases, this means we will likely have over 2,000 cases in 2019 and therefore more than 2 children in the UK are likely to die from measles. However, there is currently a media storm around the USA having multiple measles outbreaks and yet there have only been 626 cases in the USA so far in 2019 from a population much larger than the UK. Am I the only person concerned about the rates of measles in the UK?
How does measles present? Patients with measles usually have a prodromal period of high fever, cough, conjunctivitis and “cold-like” symptoms for two days prior to a rash appearing.
The rash typically appears first behind the ears and then spreads down the body; usually the severity of the rash corresponds to the severity of the illness. Most patients in the prodromal period develop bluish-white spots inside their cheeks (buccal mucosa) known as Koplik spots, which are diagnostic of measles.
Patients usually begin to improve 3 days after the rash appears and the majority are back to normal after 7-10 days.
Complications occur in 6-7% of patients and include:
Diarrhoea (80 in 1,000)
Otitis media (50 in 1,000)
Pneumonitis (38 in 1,000)*
Convulsions (5 in 1,000)
Encephalitis (1.2 in 1,000)*
Idiopathic thrombocytopaenic purpura (1 in 2,000)
*Pneumonitis and encephalitis are the most common causes of death in measles.
The most feared complication of measles is the “ticking time bomb” Subacute Sclerosing Panencephalitis (SSPE) … it occurs 5-10 years after the initial infection and cannot be predicted. It is thought to be due to chronic measles infection in the central nervous system. SSPE occurs in 5-10 per 100,000 cases overall but 18 per 100,000 where measles occurred in infancy. SSPE presents with gradual neurological symptoms such as personality change, lethargy and altered behaviour. This worsens over the next few years eventually leading to the onset of severe myoclonic jerks every 5-10 seconds, dementia and motor and sensory neurological disturbance, which can last up to 12 months. Finally the patient develops a persistent vegetative state with either flaccid or rigid paralysis. Death is inevitable.
I have looked after a patient with SSPE and it was awful for the patient, their family and the healthcare team. The patient had not been vaccinated.
How is measles diagnosed? In the UK measles is diagnosed using a buccal swab to collect saliva. The swab looks like a small bit of sponge on a plastic lolly stick, similar to those used to wet patient’s mouths with water when they are not allowed to drink (please don’t send these as swabs!). The swab kit is acquired directly from Public Health England and the sample is sent directly to the Reference Laboratory at Colindale, London, who test for measles IgM. They can also test for the virus itself by PCR if needed for epidemiological purposes. A positive measles IgM confirms the diagnosis.
How is measles treated? There is no specific antiviral for measles; supportive care with fluids, antipyretics and oxygen as required are the mainstays of treatment. The WHO recommend giving all patients with measles a course of Vitamin A as deficiency of this vitamin is associated with severe infection and higher mortality.
How is measles spread? Measles is spread via droplets from the upper respiratory tract. It is one of the most infectious viruses. It is estimated that every single person with measles infects 90 others; this is because 90% of susceptible people exposed to measles develop infection. Measles Virus can survive for about 2 hours on surfaces and as well as remain suspended as aerosolized particles for a few hours. Given that people are infectious for 48 hours before the rash appears and until 4-5 days after, is easy to see how people can be infected without even knowing they have been exposed… if measles is circulating in a community you cannot avoid it!
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I thought measles was only of historical interest, why is it back? Cases of measles are on the climb because vaccination rates are falling. In order to prevent measles from circulating within a community you need to reach a high level of “herd immunity” i.e. enough people are immunised to protect those that aren’t. The rate of immunisation to protect from measles is 95% of the population.
In the UK the current rate of immunisation with a single dose of vaccine is 92% and the recommended 2 doses is even lower, 87%. This is well below the level needed to prevent measles from circulating and there are now over 500,000 children who are not immune to measles. Some areas do particularly poorly; none of the 32 London authorities have made the 95% target in the last 5 years (2013-2018). Some London boroughs consistently have rates radically lower including Hackney and City of London (75%), Westminster (77.5%) and Kensington and Chelsea (78%). Westminster saw its rate fall as low as 69.3% in 2016-2017! Out of the 30 local authorities in the South East and East England only 1 made the 95% target. Why is that? Well…in 1998 the Lancet published (and has since retracted) the research paper by Wakefield that sparked the MMR scare; this, along with the unbalanced media coverage that followed, saw average UK vaccination rates fall to as low as only 80% in 2004. Rates are still not back up to the pre-scandal levels. If you want to know how your area is doing, then have a look at this interactive map (click to slide 3, it's the most fun!).
Those low levels of immunisation are now coming back to haunt us with all of those adolescents and young adults who should have been vaccinated in the early 2000s not actually being immune to measles.
The situation is bad in high-income countries but in fact vaccination rates worldwide are well below the required 95% target set by the WHO to gain herd immunity. Only raising global vaccination rates will actually eradicate measles, a task which is possible as humans are the only carriers of the virus. If you returned to the 1800s and told the population of London that with a vaccination measles could be eradicated, I wonder if they would have the injection?
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Controlling outbreaks? In the USA there have been 626 measles cases across 22 states in 2019, even though the USA declared measles eradicated in 2000! Technically in the USA all 50 states have laws requiring children attending public school to be vaccinated, but 17 allow exception for “personal philosophical exceptions”. New York State is taking extreme measures to try and control their measles outbreak; children less than 18 years old who have not been vaccinated are being banned from public places and anyone who breaks this rule faces a fine and 6 months in prison! In the UK the Health and Social Care Secretary, Matt Hancock, has called for new legislation to force social media companies to remove content promoting false information about vaccines. Whether this is feasible waits to be seen but it might help. Maybe responsible reporting from mainstream media like the BBC and ITN would also be helpful as they helped fuel the Wakefield debacle, yet now criticise vaccination uptake!?
...A little while after having spoken to the Paediatric Junior Doctor the Consultant Paediatrician rang the Microbiologist back. The child did indeed have Koplik spots and was now in a side room. The Paediatrician was very apologetic but had spoken to the other parents in the same area as the patient about vaccination history, whilst being careful not to breach confidentiality, and had ascertained that all the other patients and parents were immune. A list of staff had been drawn up and the ward Matron was this very minute talking to Occupational Health… at least the response after the diagnosis was excellent thought the Microbiologist….
Yep, it’s coming up to that time of year. All of Microbiology is excited as there is about to be a holiday and eggs are likely to feature in a big way… no not Easter!!! Its holiday time and people will be going to exotic countries and bringing back souvenir parasites and their eggs will be involved in working out what is wrong with them. Yep us Microbiologists’ love eggs, not just the chocolate variety. I don’t know, you lot all have chocolate on the brain :-)
Most intestinal parasites occur when someone ingests the eggs of a parasite, usually from faecally contaminated soil, which then hatch in the patient’s intestine and the parasite starts causing an infection.
Diagnosing intestinal parasite infections is actually quite difficult. There is sometimes a clue in the clinical history such as foreign travel or drinking potentially contaminated water, but most of the time in the UK we only tend to look for parasites when the clinical details say that diarrhoea has been going on for more than 2 weeks. Remember, clinical details are really important and where diarrhoea is concerned it is critical; so include travel history, pets, symptoms (e.g. bloody diarrhoea), contact with other people who are unwell and duration of symptoms.
Laboratory diagnosis of intestinal parasites There is no easy way to say this; to diagnose most intestinal parasites you have to look at poo! Okay, some labs can do molecular tests for common parasites like Giardia lamblia and Cryptosporidium parvum but for most of the others it all comes back to looking at poo.
More particularly the laboratory is looking for the eggs of the intestinal parasites in the stool sample because the adult parasite itself is usually attached higher up in the bowel where it is laying eggs into the bowel lumen which are then mixed with faeces and passed.
The eggs of parasites are bigger than bacteria but you still need a microscope to see them; parasite eggs are usually >5 micrometres in diameter but sometimes >100 micrometres, whereas bacteria are usually about 1 micrometre. Rather than using x1000 magnification on a microscope, which we use for bacteria, we tend to use x100-400 instead.
Before we look for parasites in the stool sample we need to concentrate the sample so that we get as many eggs under the microscope as possible. This is usually done using a kit that filters out as much “organic debris” (yuck) from the sample whilst concentrating smaller particles in sediment at the bottom of the tube (see picture). The sediment is then put on a microscope slide and a cover slip placed on top so that it can be looked at in more detail.
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In order to get the best chance of seeing any parasite eggs in stool it is good practice to look at at least 3 different stool samples before saying they are negative. The stool samples should be as fresh as possible, ideally within an hour of passing; otherwise the eggs may start to break down!
Appearance and size really does matter Once the sample is under the microscope it is then a case of trying to find what looks like an egg and measuring how big it is. In this complicated world, we rely on human methods. Some of the more common eggs are easily recognisable such as Ascaris lumbricoides, Fasciola hepatica and Trichuris trichuria (which I always think looks like a tea tray) but others require an experienced eye to tell them apart. If you are unable to tell them apart by appearance then size matters and measuring them with a graduated eyepiece in the microscope (not a ruler!!) allows you to compare your image to pictures in order to identify what you are seeing.
So how many of these do you recognise?
Answers at the bottom...no pun intended!
Okay the last one was chocolate, but you will be glad to know that all of the others, however grim they look, are easily treatable with the right antimicrobial. The trick though is to work out which parasite you are dealing with and for that you really do need to take a close look at poo!
Have a great Easter and remember as far as I know eating Easter eggs is not a risk factor for infection!
The patient is a young female who presented with a very high fever of 40.5oC, lethargy and not eating. The past medical history included dislocated knees due to a congenital problem requiring surgery to relocate and reconstruct the patella groove. She is not taking any regular medication, has not been in contact with anyone else who is unwell and has not travelled out of the UK. Essentially this is a case of pyrexia of unknown origin or PUO. What is PUO and what should you do about it?
What is a PUO? Pyrexia of unknown origin has a strict definition:
A temperature >38°C for >3 weeks PLUS >2 visits to hospital OR >3 days of investigation in hospital
HOWEVER, it is not enough just to admit a patient to hospital for 3 days, do nothing, and then say they have a PUO. They need to be investigated as well.
What are the common causes of PUO? In the past, infection was the most common cause of PUO but in the era of modern medicine that has changed. Two things have changed the balance of causes; people living longer and better diagnostic tests.
Microbiology investigations have improved considerably in recent years, with better bacterial culture systems, including for tuberculosis, as well as serological and molecular tests for microorganisms. As a result the number of undiagnosed infections has reduced. In addition, people are living longer and therefore the incidence of diseases like cancer, connective tissue diseases and autoimmune conditions are increasing as these are more common the older you get. Cancer diagnostics however are also improving so diagnosis is much faster and therefore cancer forms less of the PUO group than it did before.
Initial management of the patient It is critical that you don’t empirically start antibiotics unless the patient is septic or very unwell. Antibiotics will prevent the growth of bacteria and therefore make diagnosing the cause of the patient’s pyrexia almost impossible. For example, commonly used antibiotics like Co-amoxiclav, Gentamicin and Ciprofloxacin all have activity against tuberculosis (in fact they are often part of the multidrug resistant tuberculosis regimens) and will stop Mycobacterium tuberculosis growing in cultures even though these antibiotics on their own won’t successfully treat the infection… they just make it impossible to diagnose TB.
If you must start antibiotics because the patient is very unwell then treat for sepsis or the most likely alternative diagnoses.
Remember, just because you haven’t started any antibiotics doesn’t mean you shouldn’t treat the patient at all. Good supportive care must be given. If necessary give antipyretics to control the fever and make the patient feel better, consider antiemetics if the patient is vomiting, give anti-inflammatories and pain relief if necessary and IV fluids if they are dehydrated. All of this can be done while you are trying to work out what the underlying diagnosis is.
How do you investigate PUO? Keep it simple… I repeat keep it simple!
It is very tempting to rush in and test for every possible cause of PUO that you can possibly think of, and if you have access to Google it is easy to find hundreds of conditions the patient just might possibly have… don’t do it!
Start by taking a detailed history of the patient’s illness. In addition to exploring the patient’s symptoms other questions that can help include:
When did they first become unwell? – is this an acute infection over a few days or a more chronic infection like TB or endocarditis or even cancer?
Have they had a similar illness in the past? – a recurrent problem is more likely to be a connective tissue disorder or autoimmune problem
Have they had contact with anyone else who is unwell? – many infections are spread person-to-person and if someone else is ill they may have the same thing
Has anyone in their family ever had a similar illness? – some connective tissue disorders or autoimmune problems are familial
What do they do for a job? – some jobs increase the risk of infections e.g. a plumber might be at higher risk of legionellosis, a vet from zoonotic infections from animals
Do they have any particular hobbies or past times? – environmental exposure to infections can occur e.g. canoeists are at increased risk of leptospirosis, a bacterial infection transmitted by rats
Have they got any pets? – zoonotic infections such as Salmonella from reptiles, rat bite fever from rats, Capnocytophaga from dogs
Have they travelled recently or in the past? – could this be an unusual tropical or foreign infection e.g. malaria, brucella, Q Fever
Have they had any operations or do they have any prosthetic material in their bodies? – infective endocarditis is more common on prosthetic heart valves
Have they noticed any odd lumps or bumps? - connective tissue disorders often present with soft tissue swellings, lymphoma can present with abnormally large lymph glands
Have they got any swollen joints? - connective tissue disorders often present with swollen joints
Have they got any pain anywhere? – this might help localise the problem and point to where the investigations should focus, e.g. pain in the abdomen might direct imaging of the liver, urinary tract and bowel
Once you do have a good history you can formulate a differential diagnosis of what you think could be wrong with the patient and then you can work through the list of diagnoses from life-threatening and common to the more rare diseases.
When sending tests, be systematic. Do not send every test under the sun. Keep in mind that “common things are common” and even if the presentation of the disease is a bit “unusual” it is still more likely to be a “common disease presenting in an uncommon way” rather than a rare disease.
My strategy for investigating a PUO is as follows:
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Once you have a final diagnosis then you can crack on and treat it; antibiotics, cancer treatment, anti-inflammatories, immunomodulation, whatever is necessary to deal with the underlying cause.
And if you don’t find a cause and the patient gets better on their own without anything other than supportive treatment then that is also good. It might be academically frustrating but who cares, they’re better and that is all that really matters!
So our patient wasn’t started on antibiotics initially. A thorough history was taken and a comprehensive examination was performed. There was nothing to find initially and so we waited to see if they would improve with good supportive care with fluids and antipyretics.
The following day she hadn’t improved and in fact the patient was a bit worse, so further investigations were arranged. She had a full blood count, urea and electrolytes, liver function tests and a lipase in case this was pancreatitis. A urine sample was taken to look for a UTI. All of the tests came back negative.
As the patient still wasn’t improving, and was in fact worsening, we repeated some of the initial blood tests and urine screen to see if there had been any change, and moved on to second line tests including an ultrasound scan of her abdomen, as she was slightly tender around her kidneys but again these investigations didn’t identify a cause. Lack of nutrition was a concern as it was over a week since she had eaten properly, so a nasogastric tube was inserted and nutrition administered.
Two days passed and the patient had still shown no signs of improvement, no test results confirmed a diagnosis and she was getting worse so it was decided to start antibiotics empirically “just in case” this was an infection and she was given Co-amoxiclav. She was also started on a regular anti-pyretic and anti-inflammatory, an antiemetic and 3 hourly fluids. Blood tests were taken to look for infectious causes.
Over the next few days the patient started to improve a little and is now more like her normal self… she chirrups when we walk into the room and purrs when she is cuddled and made a fuss of. She has started to eat “Dreamies” treats and a bit of wet food and now growls and swishes her tail when we give her her food via her oesophagostmy (much more tortoiseshell behaviour!) … oh, did I forget to mention, the patient with the PUO is our cat Granola!
However her case does illustrate the management of PUO very well. In both humans and animals the principles are the same even if some of the causes are different:
Don’t start unnecessary antibiotics
Take a good history and perform a good clinical examination
Be systematic when investigating and remember “common things are common”
Provide good supportive care whilst looking for the cause
If the patient gets better without knowing the cause then that is a good thing
And one last thing that we learned with Granola… if you have a cat that won’t eat then don’t delay in getting them to a vet. Cats cannot fast, if they don’t eat they start to mobilise their fat stores like humans but unlike us they don’t use them efficiently for energy and instead flood their livers with the fat which can be fatal… a condition called hepatic lipidosis… they must feed even if that means feeding them through a tube until they get better…. Oh look at the time, time for another feed! …although we are now on a reducing amount with plans to remove the oesophagostmy next week.
Thank you all for your supportive comments and especially thanks to our fantastic vet team!
“Why do you think that?” asked the Microbiologist.
“Well, they have a funny skin lump and I had read recently that syphilis can mimic any other type of infection and that it’s making a comeback and so I did the test and it’s positive!”
The Microbiologist groaned to himself.
“Let me have a look at the results as well” he said.
To the Microbiologists surprise the patient did have positive syphilis serology.
“Where is the patient from?” the Microbiologist asked.
“What do you mean? They live locally” answered the GP.
“I mean where were they born? Have they lived abroad?”
“Oh, I don’t know. Why does it matter?”
“Can you give them a call and find out then call me back. This could be Yaws, Pinta or Bejel” replied the Microbiologist.
“Sorry my what? …Your's a pint of what…and a bagel? What did you say? This line is really bad” said the GP getting increasingly confused.
“Find out where they have been and call me back and then I’ll explain further” answered the Microbiologist.
So what are Yaws, Pinta or Bejel? Yaws, Pinta or Bejel are treponemal infections which are non-venereal (i.e. not spread through sexual contact) as opposed to syphilis which is also a treponemal infection but is venereal. They are caused by spirochete bacteria from the Treponema species:
Yaws = Treponema pallidum subspecies pertenue
Pinta = Treponema carateum
Bejel = Treponema pallidum subspecies endemicum
I have tried to find out the origins of the names of these infections but no one seems to know for sure. Yaws is from the Carib for “sore”, Pinta is from the Spanish for “spot” and Bejel is thought to be from the Arabic word bajal which I think means rustic or rural (maybe describing the fact that this infection is more common in people from rural areas). But am I completely wrong? Does anyone know any more? Let me know…
How do Yaws, Pinta or Bejel present? Yaws is an aggressive and highly infectious disease. The primary lesion, known as a “mother yaw”, is a painless papilloma on the face or legs (occasionally arms). This papilloma gets bigger over weeks or months becoming either ulcerated or framboesial (looking like a raspberry!). As the primary lesion starts to heal secondary lesions start to appear in the form of macules, papules and papilloma with associated inflammation of the bones (periostitis) causing “saber shins” (curved shin bones) and inflammation of the fingers (polydactylitis). Lesions tend to heal spontaneously but relapses are common. Primary and secondary yaws is known as “early yaws” which can last up to 5 years.
Late yaws occurs more than 5 years after the initial infection and affects 10-20% of those infected. It is characterised by destruction of skin and bone which whilst rarely fatal can be very disabling and socially stigmatising. Yaws does not affect any other body organs, unlike syphilis.
The primary lesion of Pinta is usually an itchy and scaly red papule with associated regional lymphadenopathy, most commonly on the arms or legs. The primary lesions often disappear spontaneously but 3-12 months later secondary lesions appear as papules or plaques of varying sizes in various areas of the body, including the face, arms and legs. These secondary lesions often go through various colour changes from blue to purple to brown before becoming pale and depigmented.
The primary lesions of Bejel are usually tiny painless papules that often are not noticed by the patient. Secondary lesions typically appear as the primary lesions start to heal, after a few months, and usually take the form of painless patches on the mucous membranes, and more papules on the rest of the body. The skin lesions can resemble those of venereal syphilis (Treponema pallidum subspecies pallidum). Late features similar to syphilis with collapse of the nasal septum and painful lesions on the soles of the feet can occur but neurological or cardiovascular disease does not occur as it could in syphilis. Mortality from Bejel is very rare.
Syphilis on the other hand presents as either primary at the point of inoculation with a chancre (painless swelling or punched out ulcer with regional lymphadenopathy) or secondary with spread from the primary site usually with a rash plus lymphadenopathy (raised mucous patches and condylomata lata - highly infectious painless wart-like lesions on warm moist sites e.g. genitals and perineal skin). Symptoms can also present 20-40 years after the initial infection, called tertiary syphilis, with gummatous, cardiovascular or neurological disease.
How are Yaws, Pinta or Bejel transmitted? Yaws primarily affects children under the age of 10 years in the tropics including West Africa (especially Ghana and Cameroon), Latin America, the Caribbean, East Asia (especially Indonesia, Papua New Guinea and Timor Leste) and the South Pacific Islands (including the Solomon Islands and Vanuatu). Yaws is transmitted through direct contact with the highly infective primary and secondary skin lesions.
Pinta is not very infectious and it is not known for sure how it is transmitted, though it is likely to be through direct contact with infected lesions. Black flies and other biting insects are also suspected to play a role in spreading the bacterium. Pinta is only found in isolated rural areas of the American tropics including Brazil, Peru, Venezuela, Central America and Cuba, and usually affects older children and adults.
Bejel is spread by contact with infected secretions, including eating utensils used by a person with primary Bejel which have been inadequately cleaned. Lesions are infectious until they have completely disappeared. It predominantly infects children aged 2-15 years in Eastern Europe and the Middle East.
Congenital transmission does not occur with any of the non-venereal treponemal infections.
Syphilis is primarily a sexually transmitted disease but it can also be acquired through direct contact with a chancre or other infected secretions. Syphilis can be acquired congenitally. Syphilis can be found Worldwide.
How are Yaws, Pinta or Bejel diagnosed? The diagnosis of a non-venereal treponemal infection is initially based on clinical suspicion, either due to the presence of a classical skin lesion or travel to or living in an endemic country. In the UK the main reason for considering the diagnosis of a non-venereal treponemal infection is a positive treponemal blood test in a patient who has had the blood test done to look for syphilis; further clinical suspicion is added if the patient has travelled to or lived in an endemic country. The treponemal blood tests include T. pallidum enzyme immunoassay (EIA), T. pallidum particle agglutination assay (TPPA), T. pallidum haemagglutination assay (TPHA), and T. pallidum IgG or IgM immunoblot. These treponemal blood tests do not distinguish between the different treponemal infections (Syphilis, Yaws, Pinta or Bejel) and remain positive for life and so a positive test in these patients is unable to say which treponemal infection the patient has had. These patients also have raised non-treponemal tests such as the Rapid Plasma Reagin tests (RPR) which can also make you think the patient might have syphilis.
Traditionally infection would be confirmed through the observation of spirochete bacteria in fluid or tissue from skin lesions using dark ground microscopy or immunoflourescent antibody. These observations combined with the travel history to give the likely bacterium. Now, in the UK most laboratories no longer have the equipment or expertise to do dark ground microscopy and so the main stay of diagnosis is PCR on infected fluid or tissue which is able to distinguish the different diseases.
How are Yaws, Pinta or Bejel treated? The easy thing about managing the non-venereal treponemal infections is that the treatment is the same whichever bacterium is causing the disease. Yep really after all that the treatment is the same! But Microbiologists do like to grow and identify these things!! The treatment is either a single dose of IM Benzathine Penicillin G (<10 years old 1.2 million units, >10 years 2.4 million units) OR a single oral dose of Azithromycin (30mg/kg max. 2g). Note: Penicillin resistance can occasionally occur but Azithromycin resistance has not been yet been seen.
All patients should have repeat RPR tests done at 6 and 12 months. If the RPR does not drop more than 2 fold or goes up at 12 months then the patient should be retreated.
“Yours a pint of what…and a bagel? This line is really bad” Meanwhile the GP called their patient then redialled straight back to the Duty Microbiologist. “Sorry that line was terrible, I thought you wanted a pint of ale and a bagel!” said the GP chuckling away… “I did call the patient though and they were originally from Brazil, does that help?”
The Microbiologist explained his clinical suspicion to the GP, who nodded knowingly but had never thought of Yaws, Pinta or Bejel as possible diagnoses. On further questioning of the GP by the Microbiologist, it turned out that the patient’s skin lesion had a bluish colour to it. Finally a biopsy of the lesion was arranged through the local dermatology department and the diagnosis was confirmed as Pinta by PCR. The patient was given a dose of oral Azithromycin and had follow up blood tests at 6 and 12 months. By 12 months the RPR had dropped considerably and the GP was able to reassure patient that they had been cured.
The Microbiologist put the phone down and muttered “a pint of ale and a bagel” …we don’t make everything up!
The Bug Blog has been on holiday; okay you know this because there have been no blogs for 4 weeks or so. Having finally finished the 3rd Edition of “Nuts & Bolts” we went on holiday to Costa Rica to see what wildlife we could see; although Costa Rica only represents 0.03% of the World’s land mass it contains 6% of its biodiversity!
We were really lucky. We saw all sorts of creatures from coatis and kinkajous (possibly the cutest animal ever!) to red-eyed tree frogs, massive cane toads, scarlet macaws and even the resplendent quetzal.
One of the critters you see all over Costa Rica, in fact all over tropical America, is the Leafcutter ant. Leafcutter ants are a curious species of ant. They are seen forming long lines across the rainforest floor carrying oversized pieces of vegetation on their backs. Leafcutter ants form large, complex societies in underground nests more than 30m across, with smaller radiating mounds extending out to a radius of 80m. A whole nest complex can cover up to 600m2 and contain eight million individual ants! But what does this all have to do with Microbiology I hear you ask?
Well the particular Leafcutter ants at La Selva Biological Station, a protected area of rainforest dedicated to research and study of this special ecosystem, and a place I went on a guided walk with a ranger, has studied these ants and found some new microbiology! La Selva is a special (and very wet) place in Sarapiqui, Costa Rica.
But back to the ants… Leafcutter ants don’t actually eat the leaves they collect, they are farmers. They use the leaves to produce compost; they use the compost to “feed” and grow a fungus which they then eat. Did you know there are 47 different species of Leafcutter ant and all eat fungi from the Lepiotaceae family (each species of ant eats a slightly different type of fungus)? OK so what has this fungus got to do with clinical microbiology…honest it’s explained a little later! …
In order for the ants to farm and grow fungi successfully, it is really important they do not bring back bits of leaf accidentally “contaminated” with a different fungus which might damage their crop. This is especially true if the leaf is contaminated with the fungi Escovopsis spp., which lives and feeds on other fungi! The ants therefore need some way of cleaning the leaves and preventing this contamination from happening. In order to protect their crop the Leafcutter ants are symbiotically colonised with a Pseudonocardia spp. bacterium. This bacterium produces an antifungal which kills the Escovopsis spp., how cool is that!? This previously unknown antifungal was discovered at La Selva in Costa Rica and they called it Selvamicin...
Apparently the researchers collected the Pseudonocardia spp. bacterium from two adjacent nests of Leafcutter ants and “screened them” for antimicrobial compounds. Fascinating, I would love to know how they did this… how on earth do you swab a leafcutter ant? I can imagine having to chase it around the laboratory without accidentally squishing it with the swab, or maybe they have a “swab trap” like a camera trap…? Who knows??
Does this have any clinical relevance? Yes! Selvamicin is a polyene antifungal, similar to Amphotericin B and Nystatin which we already use in clinical microbiology. Selvamicin has been shown to be active against Candida spp., Saccharomyces spp. and Aspergillus fumigatus. I presume it has no activity against the Lepiotaceae spp. which the ants are trying to grow; as clearly that would be a poor evolutionary step!
Although Selvamicin is a polyene antifungal, it is different to Amphotericin B and Nystatin in some important areas, especially it’s mechanism of action and its water solubility.
Mechanism of Action So far we don’t yet know how Selvamicin works; we do know it is different to the currently used polyenes. Whereas Amphotericin B and Nystatin interact with ergosterol in the fungal cell membrane, essentially behaving like a detergent by making holes in the membrane, Selvamicin does not. This is important because it means Selvamicin won’t be affected by mechanisms that lead to resistance through changes in ergosterol synthesis.
Water solubility Neither Amphotericin B nor Nystatin is available orally because of their poor solubility; this means they cannot be absorbed from the gut. Selvamicin however has a 300-fold better solubility; so it probably will be orally bioavailable. This could be a game changer because currently only the azole antifungals are available orally. Therefore at the moment, if a patient has an azole resistant infection, they would have to be admitted for intravenous treatment as no other oral agent is available; a second class of oral antifungal would be brilliant.
And another thing… Something slightly peculiar that the researchers at La Selva observed with Selvamicin is that in one of the Leafcutter ant nests the genes for producing Selvamicin were part of the chromosome of the Pseudonocardia spp. whereas in the other nest the genes were in a plasmid (mobile genetic element). The fact that the gene is found in both a chromosome and a plasmid suggests to me that it is part of a mobile genetic element that can move between bacteria. New genes can be added to either chromosomes or plasmids through the action of transposons which are genetic sequences that “help” small segments of genes move between larger sequences of genes. It also implies that Selvamicin production wasn’t originally part of Pseudonocardia spp. genetics and that it has been acquired from somewhere else.
So if it was not part of the original genetics where did it come from? Are there other, as of yet, untapped resource of antimicrobials out there in the jungle? I think I need a sabbatical to go and play in the rainforest, I mean “undertake some serious important research” … of course!
In the meantime, before I get approval for my sabbatical, the 3rd edition of Microbiology Nuts and Bolts should be available 2nd April, both on Amazon and now through normal bookshops as well. If you have recently purchased a 2nd edition we will be making any important changes and new content available online, as we did when we released the 2nd edition. We recognise how frustrating it can be to purchase a book just before a new edition is released. In fact this is one of the main reasons we are still self-publishing, because Elsevier would have published the book but they specifically said we couldn’t release free updates and so we had to say no to their offer. But that’s okay; MNB3 is coming… watch this space!
NB Thanks to the Editor Chief in Charge (aka my wife) for her tremendous efforts to get MNB to its 3rd edition…
“I don’t know what happened” she cried to the Paediatrician, “he was just a bit irritable when I put him to sleep last night and had a bit of redness around his mouth, but this morning his skin is falling off!” She then dissolved into floods of tears.
The Paediatrician took one look at the blisters and broken skin around the baby’s umbilicus and nappy area and asked “could he have been scalded with hot water at all? He looks burnt!
Through the mother’s sobs the Paediatrician could just about make out the negative answer.
“Okay, this is an infection called Staphylococcal Scalded Skin Syndrome. Let’s get your baby started on antibiotics and send off some tests. We’ll get you both up to the ward and go from there” the Paediatrician said as calmly as possible.
“Is he going to be scarred for life?” the mother asked.
“No, he won’t be scarred for life” said the Paediatrician, whilst thinking that the trauma of the whole thing was likely to mentally scar the baby’s mother for life instead!
Staphylococcal scalded skin syndrome (SSSS), or Ritter disease as it’s also known, is a toxin mediated disease due to the bacterium Staphylococcus aureus. The toxins act on the zona granulosa of the epidermis, interfering with a protein in desmosomes, the organelles that help anchor keratinocytes to each other (I’ve found a picture for you! But essentially keratinocytes are the main cells of the outer layer of skin). This results in the formation of fragile blisters (bullae) that have often broken down by the time the child presents to their family doctor or to the hospital. The result is that the child looks like they has been scalded and is losing their skin.
Click for larger image
Note: the S. aureus is not in the skin lesions, this is not cellulitis. The bacterium is sitting somewhere else in the body, not usually causing an inflammatory process locally, BUT producing toxins which disseminate around the body and target the keratinocytes. It is rare to find the original focus of infection and source control (e.g. draining abscesses) is not normally necessary or possible.
SSSS is more common in neonates and children than adults, and especially newborn babies, because they do not have a fully developed immune system. They do not have antibodies capable of neutralising the toxin (which adults often develop through exposure later in life) and their renal function is often not good enough to help them pee out the toxins. In adults SSSS tends to only occur in the immunocompromised or those with renal failure for the same reasons as in children, although adult presentation even in these groups is less common.
How does SSSS present? Neonates tend to present 3-7 days after birth. They are usually febrile and irritable. An area of redness develops on the skin (erythema), often either around the mouth or umbilicus, which then becomes blistered 1-2 days later. Blisters also start to form in areas of mechanical stress such as the flexural creases (groin and elbow), hands, feet and buttocks. The blisters then break down leaving areas of underlying raw tissue much like a burn. Infected children can have mucosal hyperaemia (increased blood flow causing redness) which often mimics conjunctivitis.
Like burns, these areas of desquamation are very painful. In fact SSSS looks so much like burns that there is often an initial concern that the child might have been burnt or scalded with hot water and raises concerns of non-accidental injury (child abuse).
An important distinguishing feature of SSSS from the main differential diagnosis of Toxic Epidermal Necrolysis (TEN) is that in SSSS the mucous membranes are not involved. TEN is similar in presentation to SSSS but is a non-infectious drug-induced skin disease which although rare can be life-threatening. If you were to biopsy a lesion, which is rarely necessary, the histology would show sloughing of only the upper layers of the epidermis in SSSS whereas in TEN there is subepidermal splitting and full-thickness epidermal necrosis.
Fortunately scarring doesn’t occur in SSSS as the splitting of the epidermis occurs intradermally not subdermally (as in TEN) so parents can be reassured that their baby won’t be scarred for life as a result of the infection however horrendous the skin looks.
How is SSSS diagnosed? The main method of diagnosis is clinical. It is very distinctive. It is important to make sure the S. aureus hasn’t spread anywhere else, so blood cultures should be taken as well as skin swabs from involved areas of skin. DO NOT use a single swab moving from lesion to lesion, use a single swab for each individual area of broken skin; if one area of skin is infected (usually secondary infection) and you swab this area and then move to other areas you will spread the infection to all of them! Remember the skin lesions of SSSS are normally sterile, the bacterium is somewhere else releasing toxin into the body not in the skin itself.
If it is critical to distinguish SSSS from TEN then a biopsy can be taken for histology to look where the epidermis is being split, but this is rarely required.
How is SSSS treated? Children with SSSS often need to be admitted to hospital for assessment, as the area of broken skin can be extensive and fluid balance can be a problem. Some of these children require IV fluids as part of their initial care.
Intravenous antibiotics targeting S. aureus should be started as soon as possible and when the child has started to improve they can be switched to oral antibiotics, for a total of 10 days. However, older children who are eating and drinking well can often be treated just with oral antibiotics.
2nd line (if 1st line contraindicated)
If high prevalence of community MRSA*
IV Teicoplanin OR IV Vancomycin
*The UK has a low prevalence of community MRSA whereas some areas of the World e.g. USA, have high rates.
The broken areas of skin should also be protected with emollients such as ointments or creams to help keep them moist and prevent secondary infection. These will also help reduce the pain as it is often air getting to the area of broken skin that triggers the pain response.
Pain relief with Paracetamol is often required but non-steroidal inflammatory drugs e.g. Ibuprofen should be avoided as they can impair renal function and potentially make the infection worse.
If treated promptly and effectively SSSS is not usually fatal in children (mortality <5%) although in adults the mortality is said to be higher usually because there is some underlying immunosuppression in this patient group.
Infection control All children with SSSS should be isolated in a single room. Good hand hygiene is essential as there is a high outbreak potential of this type of infection in hospitals, nurseries and schools. It is also good practice to wear gloves and aprons to protect yourself when caring for these children in hospital.
So our baby was admitted to the ward and started on IV Flucloxacillin whilst his mother was made a strong cup of tea. Two days later the baby’s skin was looking much better and they were changed to oral Flucloxacillin and allowed to go home. Later that afternoon the skin swab results came back showing the presence of S. aureus. Both the mother and her baby made full recoveries and neither had long term scars.
“Can I discuss an unwell baby?” asked the Neonatal Registrar.
“Of course, what’s the story?” replied the Microbiologist.
“We have a baby who is just over 24 hours old. They were born at term in good condition but started to grunt and looked mottled by 4 hours. We brought them to the Neonatal Unit, did blood cultures and started IV Benzylpenicillin and Gentamicin as per guidelines but they’re not really improving. Do you think we need to change the antibiotics? Has anything grown in the blood culture?”
The Microbiologist chose to ignore the last question as blood cultures are incubated in an automated incubator which scans the bottles every 10 minutes. If the blood culture where positive then it would have been phoned already.
“Is the baby’s mother okay? Have there been any problems during the pregnancy. Was the mother fully vaccinated? Was the labour normal? Is there anything else you’ve noticed about the baby, any odd lumps, bumps or spots?” asked the Microbiologist.
“Normal straight-forward pregnancy” replied the Registrar. “Labour was a bit tricky and there was some fetal distress but nothing too dramatic. Not a lot to find on examining the baby, just a few small bumps on the back of the head probably due to pressure from the head passing through the cervix.”
The Microbiologist pricked up their ears.
“Was a scalp electrode placed in labour? Do the bumps look like vesicles and are they close to the site of the electrode?”
“Now you ask, yep a scalp electrode was placed and the lumps are nearby. But so what?”
“Okay, I think this is neonatal Herpes Simplex Virus infection. Can you get a viral swab from one of these lesions? The baby needs to start IV Aciclovir as soon as possible. Does the mother have a history of HSV?”
“The mother has no history of genital herpes, surely it must be something else!” the Registrar said in a frustrated tone…thinking yet another wild goose chase by the Microbiologists, do they not have anything better to do than “make-up” clinical scenarios?
“Nope, it’s not, most reactivation of genital HSV is asymptomatic and therefore it is often not suspected. Get the swabs and start the Aciclovir and then I’ll explain more…”
What is neonatal Herpes Simplex infection? Neonatal Herpes infection occurs shortly after birth, usually within a few days, caused by genital Herpes Simplex Virus (HSV) acquired from the baby’s mother. Most infection is due to HSV 2 which is the most common cause of genital herpes. HSV 2 infection is more severe than HSV 1 (normally the cause of oral or orolabial herpes infection).
Genital herpes is a sexually transmitted infection which is often asymptomatic but can also presents with painful ulcers. After the primary infection, whether it is treated or untreated, HSV sits latent in the local sensory nerve ganglia from which it can reactivate causing recurrent infection. The majority of reactivation is asymptomatic and shedding of virus can occur at any time. The highest risk of transferring the infection to the baby is with primary genital herpes at the time of delivery (30-50% risk) but it can also occur with asymptomatic reactivation (3% risk). Most neonatal herpes infection occurs in asymptomatic mothers!
Infection transfer usually occurs after the baby swallows or inhales virally infected fluid at the time of delivery (85%) but it can occur in-utero (5%) or postnatally (10%) from genital or orolabial herpes (therefore adults with cold sores should not kiss newborn babies). The incidence of neonatal HSV infection is commonly thought to be 1-2 per 100,000 live births in the UK but may be as high as 17.5 per 100,000 live births.
How does neonatal herpes present? The problem with diagnosing neonatal herpes is that it presents in the same way as any other type of neonatal infection. Babies are often drowsy, pale, mottled or cyanosed, can have bradycardias or apnoeas (where they stop breathing for a period of time) or may even have seizures. But these are the features of any sick baby and are not specific to neonatal herpes. In order to diagnose neonatal herpes you have to be suspicious of neonatal herpes in ANY sick baby within the first 3-4 weeks of life otherwise you will miss it.
Clues that can help diagnose neonatal herpes include:
Vesicles at the site of scalp electrodes – the HSV enters the skin at the site of the break in skin where the scalp electrode was placed; scalp electrodes are used to monitor the pH of the fetus and give an indication of fetal distress if the pH starts to drop (i.e. the fetus is becoming acidotic)
Raised liver enzymes (aspartate transaminase or alkaline phosphatase) with a coagulopathy (slow blood clotting time) due to liver damage by the virus
There are three main types of clinical infection in neonatal HSV:
Skin Eye Mouth (SEM) infection (45%), skin vesicles including infection around scalp electrodes or other sites of minor trauma, conjunctivitis and keratitis (inflammation of the cornea)
CNS infection (30%), including encephalitis, lethargy, fever and seizures
Disseminated infection (25%), sepsis syndrome with hepatitis, disseminated intravascular coagulation (DIC), low platelets and pneumonitis (any form of disseminated infection can also have the features of SEM and CNS infection)
How do you diagnose neonatal herpes? The diagnosis of neonatal herpes is based upon demonstrating the presence of HSV by taking viral swabs from skin lesions, nasopharynx, mouth, and conjunctiva as well as taking blood and cerebrospinal fluid (CSF) for HSV PCR.
One of the biggest problems for microbiology and virology laboratories is that not enough CSF is taken to do all the tests requested. Laboratories often get only a few drops in a tube with which to do cell counts, culture and PCR as well as being expected to give some to biochemistry to measure protein! It simply is not enough to do all those tests. Babies produce about 0.35ml/kg/hour of CSF therefore it is safe to take 0.2ml/kg of CSF for testing; for an average birth weight child in the UK (2.5-4kg) this is 0.5-0.8ml (about 10-16 drops).
Non-microbiological tests include a Full Blood Count (FBC), Clotting Screen and Liver Function Test. Magnetic Resonance Imaging (MRI) of the brain and an Electroencephalogram (EEG) are also important to look for brain damage as well as an Ophthalmology review to look for eye disease.
How is neonatal herpes treated? Neonatal herpes should be treated with high dose (20mg/kg) IV Aciclovir TDS as soon as the diagnosis is suspected and treatment should be started before any results are available. This is because Aciclovir is more effective the earlier it is started.
Aciclovir is a pro-drug; it is not active in its original form but is activated by the virus’s thymidine kinase enzyme. It is not active until the virus is present, but once the virus has caused damage Aciclovir cannot help repair that damage.
The normal IV treatment duration is:
SEM – 14 days
CNS or Disseminated – 21 days
A repeat CSF for HSV PCR should be taken before stopping IV Aciclovir in babies with CNS infection and if this remains positive a further week of IV Aciclovir should be given and the CSF repeated again. The IV Aciclovir should be continued until the CSF HSV PCR is negative.
Before the availability of Aciclovir the mortality from neonatal herpes was as high as 75%, with 90% of survivors having long-term neurological damage. With treatment the mortality and long-term complications are related to the type of infection:
Type of infection
Can neonatal herpes be prevented?
Mother: if a mother has active genital herpes at the time of labour they should be started on IV Aciclovir and the baby should be delivered by caesarean section within 4-6 hours of rupture of membranes. This significantly reduces the risk of neonatal herpes but does not completely prevent it; remember 15% of neonatal herpes is not acquired by passage through the genital tract, 5% occurs in-utero or 10% postnatally from genital or orolabial herpes.
Baby: any baby born (natural or caesarean birth) to a mother with active genital herpes should be started on IV Aciclovir after birth and this should be continued until infection has been ruled out as for the diagnosis of HSV above (swabs and CSF).
Any baby born to a mother with a history of recurrent genital herpes should have nasopharyngeal, mouth and conjunctival surface swabs taken to look for exposure to the virus and they should be observed for signs of infection until these swabs come back negative. If the surface swabs are positive the baby should have a full screen including blood and CSF; if negative the parents should be warned about the clinical features of neonatal herpes and the urgent need to return to hospital if these occur over the next 4 weeks.
Some experts recommend oral Aciclovir from 36 weeks gestation until after delivery for all mothers with a history of genital herpes infection to prevent the development of active lesions around the time of delivery. The efficacy and safety of this approach are not known but it may be helpful.
What about preventing recurrence in the baby? Following the initial neonatal herpes infection the virus remains in the sensory ganglia of the nerve cells and can reactivate. This is very common when the initial infection occurred in the neonatal period (birth to 28 days). Between 50-80% of babies will have recurrent episodes of herpes infection in the first year of life with 1-12 episodes per baby; ≥3 episodes in the first 6 months is associated with greater long-term neurological damage.
Because of the risk of recurrence and the damage this can cause, all babies who have had neonatal herpes should be given 6-12 months of oral Aciclovir to prevent such recurrences. This reduces the risk of recurrence but doesn’t completely prevent it from happening so parents need to be aware and return to hospital if symptoms of herpes infection recur.
So our baby was started on IV Aciclovir as soon as the registrar put the phone down. Swabs from the skin lesions confirmed HSV 2 infection but fortunately for the baby the blood and CSF PCRs were normal. They were treated with 2 weeks of IV Aciclovir and sent home on a planned 12 months of oral Aciclovir. At the 1 month review the baby was doing well and no further episodes had occurred. Review as an outpatient will continue for at least 12 months but it is hoped that the baby will be fine in the future.
Maggots are fly larvae. Their life cycle goes like this: flies are attracted to food and other rubbish on which they lay their eggs; later the eggs hatch into maggots, which turn into flies. You may be wondering if you have eaten that picnic sandwich which a fly had just landed on (and possibly laid its eggs), whether the eggs and maggots can survive!? Answer: larvae that might be accidentally ingested with food cannot usually survive in the gastrointestinal environment.
Maggots are not all bad however, they play an important role in decomposition, pollinating plants and providing food for other insects. They can also help solve crimes. Surely you remember Gil Grissom’s (from the TV series, CSI: Crime Scene Investigates) obsession with flies and larvae; he uses entomology to identify time of death by calculating the timeline of flies arriving, feeding and laying eggs in decomposing flesh. A lifecycle first demonstrated in 1668, by Italian physician Francesco Redi who showed that maggots do not “just appear” but that maggots turned into flies, which laid eggs that turned into more maggots.
Maggots can also heal wounds. Larval therapy has been known about for hundreds of years. It was used by ancient Mayan civilizations as well as Aboriginal tribes in Australia; even Napolean’s Surgeon in about 1800 noted that certain species of flies helped wounds to heal.
Larval therapy is the use of live, disinfected maggots from specific species of flies that are deliberately put into wounds in order to remove dead necrotic tissue therefore assisting wound healing. The most commonly used species of maggot for medical therapy is Lucilia sericata, the common green bottle fly larva.
The “magnificent” thing about the larvae of Lucilia sericata is that they also produce antimicrobial compounds… who would have guessed? Well it actually makes sense if you think about it further. The maggots usually survive in the environments of dead and necrotic tissue; these are potentially hostile places as these conditions are also where bacteria thrive. As these bacteria grow and multiply much faster than the maggots, the bacteria might be expected to out-compete the maggot for resources such as food. In order to stop this happening the maggots have developed a form of defence mechanism against the bacteria, manufacturing lethal compounds which they direct towards the bacteria. This is much the same way as fungi do, which are the traditional source of antimicrobials. Nature is really rather clever in that way.
A recent paper in the Journal of Antimicrobial Chemotherapy (JAC) has described two possible antimicrobials for future development derived from the larvae of Lucilia sericata. The JAC is an excellent scientific journal about antimicrobials but unfortunately this article will not be free to access by all, you’d have to become a member of the British Society for Antimicrobial Chemotherapy (BSAC)… which if you are interested in antimicrobials is a very worthwhile thing to do, but I might be biased as I have been a member of this society for many years. Alternatively the hospital library might be able to get you a copy.
Antimicrobial peptides (AMPs) The two compounds described in the JAC paper, called LS-sarcotoxin and LS-stomoxyn, are linear cationic antimicrobial peptides (AMPs). AMPs are part of the innate immune response (the primitive part of the immune system which is part of the early response to pathogens) of all living things but they differ between organisms. They have very variable structures and mechanisms of action although cell membranes are a common target. Because of this they are often compared to the antibiotic Colistin which also targets the cell membrane of bacteria.
Having said that, the exact mechanism of action of LS-sarcotoxin and LS-stomoxyn is not actually known. Whilst they may target the cell membrane like Colistin they do not compete for the exact same target as they show synergy with Colistin (the combination is more effective than the sum of the activity of each agent alone).
Spectrum of activity The paper’s authors tested LS-sarcotoxin and LS-stomoxyn against 114 multidrug resistant (MDR) Gram-negative bacteria isolated from hospital patients in Germany. The majority of the bacteria tested were E. coli, Klebsiella pneumoniae, Enterobacter cloacae and Acinetobacter baumanii. These bacteria are either notorious for being resistant as in the case of A. baumanii, or commonly found to be resistant to many antibiotics. The AMPs from maggots were principally active against Gram-negative bacteria and this makes sense as these are the types of bacteria likely to colonise wounds and dead tissue and the main competitors for the maggots.
The two AMPs have been previously shown to have no activity against Gram-positive bacteria and Candida spp., but that’s fine as it is the fight against Gram-negative bacteria where we really need new antibiotics.
LS-sarcotoxin showed excellent activity against E. coli, E. cloacae, Klebsiella spp., Salmonella enterica, Citrobacter freundii and Acinetobacter spp., although it had little activity against Pseudomonas aeruginosa.
LS-stomoxyn on the other hand had good activity against Pseudomonas aeruginosa, A. baumanii and most of the Enterobacteriaceae with the exception of K. pneumoniae.
Even bacteria which have a lot of resistance mechanisms e.g. to beta-lactams, aminoglycosides and fluoroquinolones were still sensitive to the AMPs
Neither AMP was active against the Gram-negative bacteria Proteus mirabilis, Stenotrophomonas maltophilia, Morganella morganii or Serratia spp.
In order to assess experimentally how LS-sarcotoxin and LS-stomoxyn might behave in a human body the AMPs were tested in the presence of sodium chloride and human serum. Surprisingly the addition of sodium chloride and human serum made the AMPs much more effective, reducing the minimum inhibitory concentrations (MICs) by 16-128 times depending on the bacterium tested. This means you would need 16-128 times less antibiotic when using it in the human body and that’s pretty magnificent! Most antibiotics are not affected by sodium chloride or human serum like this.
Selection of resistance Resistance is an emerging threat to all antibiotics so determining early if the target bacteria can easily become resistant to the new antibiotic compound is increasingly prudent! The authors tried to “make” bacteria resistant to the AMPs by serially passaging bacteria against low levels of the AMPs; essentially they grew the bacteria in low concentrations of AMP over 30 days in order to try and select out resistant mutants. Typically when E. coli and P. aeruginosa are passaged with Colistin the bacteria develop a 100x increase in MIC i.e. they would become resistant to normal and high levels of antibiotics. This has been demonstrated by Harvard University in this YouTube video of showing E. coli developing resistance to an antibiotic over only 10 days!
However, with LS-sarcotoxin and LS-stomoxyn neither E. coli nor P. aeruginosa became resistant during a 30 day period, suggesting resistance to these AMPs may not occur readily in real life use.
Are these AMPs toxic? Maybe this should be the first question asked…but it often isn’t! In the JAC paper the authors undertook a number of experiments to look for toxicity by adding low and high concentrations of the AMPs to cell cultures of human cells. No haemolytic, cardiotoxic or other toxicity issues were demonstrated. In addition, when the AMPs were injected into mice for stability studies, no toxicity was seen. Okay, these are preliminary studies but toxicity at this stage would be the end of this area of research! A dead patient with a cured infection is not a good outcome… sometimes Doctors need to remember this! (See organ failure blog).
So what are the drawbacks to these magnificent maggot compounds? There are two main drawbacks from this initial study of LS-sarcotoxin and LS-stomoxyn. The first is the lack of activity against ALL Gram-negative bacteria. I know I’m being greedy but with good reason. If LS-sarcotoxin and LS-stomoxyn showed good activity against all of the Enterobacteriaceae then they would be excellent antibiotics for the empirical treatment of Gram-negative infections such as UTIs or intra-abdominal sepsis, however when there are significant Gram-negative bacteria that are NOT COVERED (e.g. P. mirabilis, S. maltophilia, M. morganii, Serratia spp. and P. aeruginosa) then the LS-sarcotoxin and LS-stomoxyn would either have to be used in combination with other antibiotics (which is feasible) or would have to be reserved for when the exact bacterium was known.
The second drawback is much more problematic. LS-sarcotoxin and LS-stomoxyn are unstable in plasma; in the mouse testing the compounds could only be detected for about 5-15 minutes. This is not long enough for them to be active against bacteria in the blood stream. This could be a major problem. Or it may be that the AMPs are binding to protein in the blood and therefore cannot be detected but still have activity; I’m sure there will be further work to fully ascertain the pharmacokinetics.
So it looks like maggots may be the future for anti-Gram-negative antibiotics. Two compounds, LS-sarcotoxin and LS-stomoxyn, derived from the green bottle fly larvae show good activity against many MDR Gram-negative bacteria. I for one look forward to reading the results of the further work to see if these compounds might be suitable as future antibiotics.
Could our new antibiotics look like this...?
Profiling antimicrobial peptides from the medical maggot Lucilia sericata as potential antibiotics for MDR Gram-negative bacteria. R. Hirsch, J Wiesner, A Marker, et al. J Antimicrob Chemother 2019; 74: 96-107
P.S. If you are dreaming of maggots, apparently it means that you are not able to recognise (or deal with) a problem that is bothering you in your waking life... for me these dreams tend to occur on call after dealing with MDR Gram-negative infections!