The official blog of the International Journal of Epidemiology. The IJEblog contextualizes and provides insight into epidemiological research related to the Journal's publication programme. It aims to make the latest epidemiological discoveries accessible to an audience beyond the Journal's traditional readership, encourage debate, and help authors maximise the impact of their research.
For children in low-income countries, diarrhoea
remains a major cause of death and can lead to long-term health consequences. Accurate
estimates of childhood diarrhoeal illness are crucial to evaluating the success
of campaigns to defeat diarrhoea and improve health in countries where the
burden of diarrhoea is high.
In our study, recently published in the IJE, we found that caregivers may underestimate diarrhoeal diseases in children aged under 5 years when asked to recall whether the children had diarrhoea in the previous 2 weeks. Compared with a 1-week recall period, there was a consistent underestimation of the prevalence of diarrhoea across five countries in sub-Saharan Africa.
Our analysis pooled over 80,000 household surveys from two similarly administered nationally representative surveys that use different recall periods for ascertaining caregiver-reported diarrhoea: Performance Monitoring and Accountability 2020 (PMA2020), which uses a 1-week recall; and the Demographic and Health Surveys (DHS), which use a 2-week recall. The PMA2020 survey was designed to be methodologically similar to the DHS in almost every aspect, and the two surveys are ideal for comparison of this important outcome. We found a childhood diarrhoea period prevalence of 21.4% using the 1-week-recall PMA2020 data, compared with a potentially underestimated 16.0% when using the 2-week-recall DHS data.
The finding that fewer diarrhoea episodes are
identified when using a longer recall period initially appears counterintuitive.
Researchers frequently use 2-week recall periods to try to identify a greater number
of cases. However, in places where diarrhoea is common, a longer recall period may
lead to caregivers forgetting more diarrhoea events. It may be easier for caregivers
to remember diarrhoeal symptoms in only the past 7 days, which is a standard unit
of time in many cultures, and this might have led to greater accuracy from the PMA2020
A contributing factor to childhood diarrhoea
is high faecal contamination due to lack of water and sanitation infrastructure
in communities. As countries make investments to improve sanitary conditions, accurate
measures of diarrhoeal disease will be important to track health outcomes. We
found that children under 12 months of age were at greatest risk of diarrhoeal diseases
and that lack of access to safely managed sanitation facilities in the household
was the greatest risk factor for infection. A risk factor analysis using the
1-week recall PMA2020 data determined that improved sanitation reduced the odds
of diarrhoeal disease, while access to improved drinking water did not.
Consistent with previous work, our findings underscore the importance of prioritising investments in sanitary infrastructure. Comprehensive investments in toilet construction and safe management of faeces will be important to improve the health of children and communities. Equally important is ensuring those toilets are used and changing individual behaviours to end open defecation.
More work is also needed to determine the optimal recall period for childhood diarrhoea in national health surveys. An ideal comparison would include the same question asked twice in the same survey – one question using a 2-week period and another using 1 week. It is important to further improve outcome measures for childhood diarrhoea to assist health ministries as they make large-scale efforts to defeat diarrhoea as a leading cause of childhood deaths.
Overbey KN, Schwab KJ, Exum NG.Comparison of 1-week and 2-week recall periods for caregiver-reported diarrhoeal illness in children, using nationally representative household surveys. Int J Epidemiol 2019; Mar 25. https://doi.org/10.1093/ije/dyz043.
Katie Overbey is a PhD candidate in the Department of Environmental Health and Engineering at the Johns Hopkins University Bloomberg School of Public Health. Her research focuses on the fate and transport of norovirus in food, water and the environment.
Kellogg Schwab,PhD, is the Abel Wolman Professor in Water and Public Health in the Department of Environmental Health and Engineering at the Johns Hopkins University Bloomberg School of Public Health and Director of the JHU Water Institute. His research focuses on water reuse and infectious diseases around the world.
Natalie Exum, PhD, is an assistant scientist in the Department of Environmental Health and Engineering at the Johns Hopkins University Bloomberg School of Public Health and Deputy Director of the JHU Water Institute. She is also the Senior Technical Advisor for Water, Sanitation and Hygiene (WASH) for PMA2020’s mobile health data collection platform. Her research focuses on environmental faecal contamination and childhood enteric infections.
Suman Chakrabarti, Md Tajuddin Khan and Samuel Scott
Respiratory infections are the most common
chronic disease in children globally and a leading cause of death in developing
countries. This situation is exacerbated by air pollution.
Air pollution in northern India, mainly New Delhi and the neighbouring states, is exacting a toll on the health of residents, making global headlines and highlighting the severity and extent of this public health disaster in one of the world’s fastest-growing economies.
A contributory factor to air pollution in northern India is the harmful practice of crop residue burning — when farmers burn the crop residue to clear fields before sowing a new crop. Although banned by the Indian government in 2015, this practice remains prevalent in many parts of the northern Indian states of Punjab, Haryana and Uttar Pradesh.
Credit: Neil Palmer (CIAT). Burning of rice residues after harvest, to quickly prepare the land for wheat planting, around Sangrur, SE Punjab, India (Creative Commons Attribution-Share Alike 2.0 Generic licence)
In our study recently published in the IJE, we found a link between crop residue burning and acute respiratory infection and estimated its economic and health costs. We analysed health data from more than 250,000 people of all ages residing in villages and cities in India. Using NASA satellite data on fire activity to estimate the health impact of living in areas with intense crop burning, we found that the frequency of reported hospital visits for acute respiratory infection symptoms paralleled the number of fires observed by satellite: as crop burning increased, respiratory health worsened.
Crop residue burning was the leading risk factor among those we examined for acute respiratory infection in India, and economic losses associated with the health effects of crop residue burning were estimated at about USD35 billion per year. When combined with firecracker burning, the economic losses are nearly USD152 billion, or 1.7 per cent of India’s GDP over five years.
In districts where crop residue burning is intense, residents, especially children under 5 years of age, are three times more likely to visit the hospital for symptoms of acute respiratory infection. We found that it wasn’t only the residents of Delhi, but also women, children and men living in the rural areas of Delhi’s neighbouring state, Haryana, who are the first victims of crop residue burning. Much of the public discussion about ill effects of crop residue burning ignores this immediately affected vulnerable population and focuses only on residents of Delhi.
During certain times of the year, coinciding with the onset of winter in northern India, levels of airborne particulate matter in Delhi spike to 20 times the safe threshold proposed by the World Health Organization. Smoke from burning of crop residue in northwestern India has been estimated to contribute up to 78% of the enhancement in small particulate matter in Delhi on certain days.
Our study found that exposure to vehicular
pollution, open drains, cooking with biomass and urban living are some of the
other leading risk factors for acute respiratory infection.
Even though biomass burning is practised in the United States and several developed countries in Europe, it has become a major health concern in India due to its negative impact on air pollution. The Indian government has demonstrated an interest in combating air pollution and respiratory illness but, so far, has fallen short in addressing the air quality crisis.
As Indian farmers face tough times, convincing them to change their practices will require full cooperation from the highest levels of government. Our study suggests that targeted government initiatives to improve crop disposal practices are worthy investments. Programs and policies must simultaneously address indoor and outdoor pollution through a combination of bans and agricultural subsidies. Other important interventions for improving respiratory health are increasing household access to clean cooking fuels, electricity and improved drainage systems.
Despite efforts from the Indian government, farmers continue to burn crop residue because of a lack of convenient and affordable alternatives. Eliminating crop burning will not only improve human health but will also contribute to soil and plant biodiversity and reduce greenhouse gas emissions.
Chakrabarti S, Tajuddin Khan M, Kishore A, Roy D, Scott SP. Risk of acute respiratory infection from crop burning in India: estimating disease burden and economic welfare from satellite and national health survey data for 250 000 persons. Int J Epidemiol 2019; Feb 28. https://doi.org/10.1093/ije/dyz022.
Samuel Scott is a researcher
at the International Food Policy Research Institute, New Delhi, India. Suman
Chakrabarti and Md Tajuddin Khan are doctoral candidates at the University of
Washington and Oklahoma State University, respectively.
Over an average week, adults in the United
Kingdom living with chronic disease spend 61 minutes (9%) less on moderate
activity — such as gardening, brisk walking and housework — and 3 minutes (11%)
less on vigorous activity — such as running and aerobics — than their healthy peers.
Perhaps this comes as a surprise. After all, few of us would question the health benefits of keeping moving and getting our heart rate racing. Physical activity guidelines, such as those developed by the UK’s National Institute for Health and Clinical Excellence, specifically refer to the importance of increasing physical activity for chronic disease management.
So why have we observed a gap in activity
levels between those living with chronic disease and those without?
Our research, recently published in the International Journal of Epidemiology, canvassed more than 96,000 adults aged 40 years or older from the UK Biobank, of whom 44% had at least one chronic disease. Among the people with chronic disease, the average age was 63.5 years for women and 65.5 years for men.
We measured physical activity levels of
both groups using accelerometers (devices that record ‘bodily movement’ and are
worn like a watch on participants’ wrists) over 7 days, then categorised their activity
by degree of intensity.
Unlike many previous studies that have
relied on self-reporting of activity, which is inevitably subjective and often
fails to capture routine or brief movements such as climbing the stairs, our
objective measure offers a more accurate and complete picture.
Indeed, some chronic diseases, such as
respiratory or cardiovascular disorders, can limit people’s capacity for
exercise, owing to a reduced supply of oxygen, while musculoskeletal disorders can
affect their ability to engage in everyday activities. Mental health disorders
might affect motivation to be active and, across the entire study population,
we found that those with mental health disorders had the lowest levels of moderate
activity, spending 2.4 hours less per week on this type of activity than those
without any chronic disease (their healthy peers were moderately active for an
average of 11.8 hours per week).
However, not all chronic conditions
directly affect capacity for exercise. Therefore, we must consider other
factors, such as the possible impact of the ‘sick role’. The very fact of
having a chronic disease seems to influence people to be less physically active.
So functional and behavioural limitations may both be at the root of this difference
Barker J, Smith-Byrne K, Doherty A, et al. Physical activity of UK adults with chronic disease: cross-sectional analysis of accelerometer measured physical activity in 96,706 UK Biobank participants. Int J Epidemiol 2019; Feb 5. https://doi.org/10.1093/ije/dyy294.
Smoking was established as a cause of lung cancer in 1950. It then took another 70 years to establish that colorectal cancer was also a smoking-related cancer. However, as of 2018, a causal relationship between smoking and breast cancer had not yet been established. It may seem strange that it is taking so long to prove that smoking is a cause of all three of the most common cancers globally. Breast and lung cancer each account for 2.09 million cases annually and colorectal cancer for 1.8 million.
Before smoking can be established as a cause of breast cancer, the association between smoking and breast cancer must first be shown in different populations. In our study, recently published in the International Journal of Epidemiology, we investigated whether the smoking-related increase in breast cancer was similar across five ethnic groups in the United States: African Americans, Native Hawaiians, Japanese Americans, Latinas and White Americans.
followed more than 70,000 postmenopausal women who were enrolled in the
Multiethnic Cohort study in 1993. The women completed a questionnaire and
reported whether they had smoked at least 20 packs of cigarettes in their
lifetime, the number of years they smoked cigarettes, the average number of
cigarettes smoked per day during the period when they smoked, and the number of
years since they quit smoking. We calculated age at smoking initiation and, for
parous smokers, the years of smoking before their first childbirth. We adjusted
our analyses by including known breast cancer risk factors (age, family history
of breast cancer, education, body mass index, age at menarche, age at first
childbirth, number of children, age at and type of menopause, post-menopausal
hormone therapy and alcohol consumption) as covariates.
Overall, 4230 of the women were diagnosed with breast cancer during the following 17 years. We made four important findings from our study. First, we found that if women smoked before giving birth to their first child, their risk of developing breast cancer later in life increased. This higher risk was confined to parous women who had started smoking more than 5 years before the birth of their first child. Second, we found that the magnitude of this higher breast cancer risk was consistent across African Americans, Native Hawaiians, Japanese Americans and White Americans. Third, we did not observe any association for Latinas, of whom only a small proportion had started to smoke before having their first child. Finally, we found that a higher risk of smoking-related breast cancer seemed to be present, and of a similar magnitude, for both oestrogen and progestorone hormone receptor tumours.
One reason that recent cohort studies find a consistent association between smoking and breast cancer is that more women than in previous generations now initiate smoking during their teens. In a study of more than 300,000 Norwegian women, we found that the mean age at smoking initiation had lowered and that the proportion of women who started to smoke before their first childbirth had increased steadily, from 62% for those born before 1946 to 94% for those born after 1955. Fortunately, most women who smoke today report that they will stop smoking when they fall pregnant and have a child. However, teenagers and adolescent women need to be made aware that their risk of breast cancer is closely associated with the number of years they smoke before having their first child. Breast cancer is such a common disease that even a small increase in risk results in many new cases. As smoking, alcohol consumption and being overweight after 50 years of age are all avoidable risk factors, breast cancer prevention is, to some extent, possible.
More than 40 years ago, scientists suggested there was biological plausibility for an association between cigarette smoking and breast cancer. They had identified nicotine, one of the major constituents of tobacco smoke, and its major metabolite cotinine in the breast fluid of non-lactating women who smoked. There are more than 70 established carcinogens in cigarette smoke and more than 20 substances that induce mammary cancers in rodents. These compounds are also found in human breast tissue. In 1982, Russo et al hypothesised that mammary tissue is more susceptible to carcinogenic exposures between menarche and the last trimester of the first pregnancy, when breast cells become fully differentiated. Our results support this hypothesis.
The results of our study, together with
those from other recent cohort studies, support the notion that breast cancer
is a smoking-related cancer. We think it is time for public health agencies to review the data on smoking
and breast cancer and reconsider whether the available evidence is sufficient to
establish smoking as a cause of breast cancer.
Gram IT, Park SY, Maskarinec G, et al. Smoking and breast cancer risk by race/ethnicity and oestrogen and progesterone receptor status: the Multiethnic Cohort (MEC) study. Int J Epidemiol 2019; Jan 18. doi: 10.1093/ije/dyy290.
Tricia L Larose, Arnulf Langhammer and Mattias Johansson, for the Lung Cancer Cohort Consortium (LC3)
Lung cancer is one of the most common cancers worldwide, accounting for 2.09 million cases and 1.76 million deaths in 2018. Two of the most prolific cancer epidemiologists of our time — Sir Richard Doll and Sir Bradford Hill — identified smoking as the biggest cause of lung cancer in their seminal report, “Smoking and Carcinoma of the Lung”, published in the British Medical Journal in 1950. Nearly 70 years later, smoking remains the predominant risk factor for lung cancer, as well as for 15 additional cancers and other non-communicable diseases.
Cigarettes contain nicotine — a highly addictive substance that induces pleasure and reduces stress and anxiety. Many current smokers would like to quit but, due to nicotine addiction, more than 80% of those who attempt to quit return to smoking within 6 months. Moreover, smoking may be a social norm in some familial or social clusters, thus reinforcing the behaviour despite the well-known negative health effects.
In our recent study published in the International Journal of Epidemiology, we studied the lung cancer risk implications of blood concentrations of cotinine — a nicotine metabolite and an objective measure of recent tobacco exposure. In particular, we measured pre-diagnostic cotinine concentrations for nearly 5500 people who were later diagnosed with lung cancer and 5500 additional matched control participants from 20 prospective cohort studies in the US, Europe, Asia and Australia. This is by far the largest study of its kind to date.
The median time between blood sampling and lung cancer diagnosis in the study participants was 6.3 years. We considered cotinine concentrations of 115 nmol/L or higher to be indicative of active smoking, between 5 and 115 nmol/L as indicative of second-hand smoke exposure, and less than 5 nmol/L as unexposed to smoking.
Our findings were threefold. First, we showed that circulating cotinine concentrations are consistently associated with lung cancer risk for current smokers, over and above that indicated by self-reported smoking exposure. Second, we showed that combining cotinine measures with self-reported smoking may help identify individuals at elevated risk of developing lung cancer, compared with relying on self-reported smoking information alone. Finally, when we compared self-reported smoking status (never, former or current smokers) with circulating cotinine concentrations, we found cotinine concentrations consistent with active smoking to be common in former smokers (cases: 14.6%, controls: 9.2%).
To evaluate the association between exposure to
second-hand smoke and lung cancer risk, we estimated odds ratios for former and
never smokers separately by comparing participants with cotinine concentrations
between 5 and 115 nmol/L (exposed) to participants with cotinine
concentrations below 5 nmol/L (unexposed). However, despite our relatively
large sample of more than 1500 former and 1300 never smoker case–control pairs,
we did not observe a risk increase for participants with circulating cotinine
concentrations consistent with second-hand smoke exposure.
Our results highlight that misclassification of
self-reported smoking status may be common in epidemiological studies. This is
an important consideration for epidemiological studies on smoking-related
diseases, as misclassification among self-reported former smokers may result in
a failure to fully account for smoking as an underlying reason for an observed
association between a putative risk factor and disease risk — a phenomenon
often referred to as “residual confounding” by epidemiologists. Considering the
impact of tobacco exposure on the risk of a wide range of diseases, as well as
its influence on most risk factors, it is virtually impossible to exclude
tobacco exposure as an underlying reason for many alleged risk factor–disease
relationships. To this end, cotinine — as an objective measure of recent
smoking intensity — offers a means to circumvent this inherent limitation of
many epidemiological studies.
The findings of our study also have important clinical implications. Risk prediction models that combine pre-diagnostic biomarker measures with other self-reported data may better identify patients who would benefit from lung cancer screening (e.g. CT screening). A recent large clinical trial has proven that early detection of lung cancer through screening can decrease mortality rates by over 20%. However, only about 50% of people who are diagnosed with lung cancer are eligible for screening using current recommended criteria. With biomarker-based risk prediction models, it may be possible to improve screening effectiveness by better identifying those individuals who are most likely to benefit from screening. Our study demonstrated that cotinine, perhaps in combination with other risk-indicative biomarkers, may be of use for that purpose.
Larose TL, Guida F, Fanidi A, et al. Circulating cotinine concentrations and lung cancer risk in the Lung Cancer Cohort Consortium (LC3). Int J Epidemiol 2018; 47: 1760-1771. https://doi.org/10.1093/ije/dyy100.
Tricia L Larose, PhDis a postdoctoral scientist with the Genetic Epidemiology Group, Section of Genetics, International Agency for Research on Cancer — the specialised cancer agency of the World Health Organization. She is cross-appointed to the K.G. Jebsen Center for Genetic Epidemiology, Faculty of Medicine and Health Sciences, Norwegian University of Science and Technology. Her work is supported by the Research Council of Norway (grant number 267776/H10). You can follow Tricia on Twitter @TricLarose
Arnulf Langhammer, MD, PhD is a medical doctor and clinician, a professor and leader of the HUNT databank. The HUNT study is one of 20 participating cohorts in the Lung Cancer Cohort Consortium (LC3).
Mattias Johansson, PhD is a scientist in the Genetic Epidemiology Group, Section of Genetics, International Agency for Research on Cancer, World Health Organization. He is the co-PI for the Lung Cancer Cohort Consortium (LC3). The LC3 was supported by the National Institutes of Health/National Cancer Institute (grant number 1U1CA155340-01) and the Australian National Health and Medical Research Council (grant number 1050198). You can follow Mattias on Twitter @Mattias31
Jennyfer Wolf, Richard Johnston, Matthew C Freeman and Annette Prüss-Ustün
Handwashing with soap after faecal contact is key to preventing disease and death from enteric infectious diseases. Our study, recently published in the IJE, is the first to provide global, regional and country estimates of handwashing with soap after potential contact with human faeces, based on representative data on access to handwashing facilities collected for monitoring of the Sustainable Development Goals (SDGs). Our results show that handwashing with soap after using the toilet or other potential contact with human faeces is poorly practised worldwide and that even the necessary equipment – handwashing facilities with soap and water – are inaccessible to billions of people.
The SDGs now explicitly include the presence of handwashing facilities with soap and water in indicator 6.2.1. Given that handwashing with soap is believed to be one of the most cost-effective public health interventions, this additional target elevates the importance of personal hygiene compared with the preceding Millennium Development Goals, which did not include a handwashing indicator. In addition, handwashing with soap – as a proxy or indirect measure for hygiene – is now also being included in burden of disease analyses, which provide a comprehensive picture of health loss from diseases, injuries and risk factors.
Although the addition of a proxy measure for hygiene is an encouraging step, the results of our analysis strongly question the approach of equating access to handwashing facilities with actual handwashing behaviour. We estimate that 74% of the world’s population have access to handwashing facilities with soap and water, but only 26% of events in which hands are potentially contaminated with human faeces are followed by handwashing with soap. Global analysis of the burden of disease needs to reflect this difference between access to and use of handwashing facilities.
Furthermore, both access to handwashing facilities and use of such facilities when they are present showed large regional variations. We estimate that access to soap and water in the home is near-universal in high-income countries, and about half of potential faecal contacts are followed by handwashing with soap and water in these settings. In contrast, in low- and middle-income countries of Africa, only about 18% of people have access to handwashing facilities in the home, and only 14% of those with access are likely to wash their hands after potential contact with faecal matter. The areas where the burden of infectious disease is highest are the same areas where handwashing is least likely to occur; even in households with the necessary materials at hand.
Novel approaches must be developed and scaled to rapidly improve access to and use of handwashing facilities, especially in low- and middle-income settings, to prevent endemic infectious diseases and to mitigate epidemics, such as Ebola virus and cholera. It is clear that simple health-based promotional approaches have not been effective in changing behaviour. We encourage the use of well-established behavioural theory, in both the formative research and intervention design phases, to address context-specific challenges and influence critical pathways for behaviour change and habit formation, such as social norms, social support, cues and reminders, and self-efficacy. Examples include the “behaviour change wheel” and the RANAS (Risks, Attitudes, Norms, Abilities and Self-regulation) approach to systematic behaviour change, both of which can be used for intervention development.
Finally, hygiene is multifaceted and considerably broader than simply handwashing, encompassing behaviour such as bathing and face washing, menstrual hygiene, food hygiene and the correct management of child and animal faeces. Public health interventions and associated monitoring schemes should widen their focus to incorporate all of these behaviours.
Jennyfer Wolf is a public health doctor with training in epidemiology and a consultant for the Department of Public Health, Environmental and Social Determinants of Health at the World Health Organization.
Richard Johnston is an environmental engineer and technical officer for water, sanitation and hygiene at the Department of Public Health, Environmental and Social Determinants of Health at the World Health Organization.
Matthew Freeman is an associate professor in the Department of Environmental Health at the Rollins School of Public Health at Emory University.
Annette Prüss-Ustün is an epidemiologist and team leader of Assessment of Environmental Health Impacts at the Department of Public Health, Environmental and Social Determinants of Health at the World Health Organization.
Alba Ripoll Gallardo, Barbara Pacelli and Elias Allara
Population growth and urbanisation of seismic areas are leading to a constant increase in the health-related and economic toll of earthquakes. In 2014 alone, 324 natural disasters were reported worldwide, resulting in 141 million casualties and nearly $100 billion in damage. Geophysical disasters, including earthquakes, accounted for about 10% of these events.
Although the impact of earthquakes in the response phase – that is, immediately or shortly after the main seismic event – has been well studied, we have little knowledge of the effects of earthquakes in the medium and long term. This uncertainty may cause inefficient planning of post-earthquake epidemiological surveillance, resulting in potential underestimation of public health needs.
For these reasons, in our review recently published in the IJE, we attempted to systematically organise the extant epidemiological knowledge about the post-response phase – that is, at least one month after the main seismic event. We searched common medical databases as well as several sources of grey literature, and we set no limitations in our search string regarding the diseases or earthquake investigated.
From the results of our search, we analysed 52 studies conducted over the past 30 years, involving individual-level data from more than 80,000 participants, and aggregated data – in which individual participant characteristics were not available in the denominator – from more than 50 million people. We included observational studies focusing on health indicators measured at least one month after earthquakes occurred in high-income countries. Reasons for exclusion included lack of a comparison group, inability to distinguish the health effects of the earthquake from those of other disasters that occurred simultaneously, and lack of quantitative data.
In our analysis, we found increased all-cause mortality, with strong evidence of greater mortality rates from myocardial infarction and stroke, and higher mean levels of glycated haemoglobin among people exposed to earthquakes compared with those who were not exposed (see figure below). We also found evidence of an increase in gastric ulcers and consumption of antipsychotic medications, although these findings were based on individual studies, as well as mixed evidence about possible effects of earthquakes on antidepressant consumption and infectious diseases.
These findings indicate the need for improvement of current epidemiological surveillance systems.
First, our work shows that extending the follow-up after the recovery phase (at least 24 months) is useful because multiple health conditions have been associated with earthquakes in the long term.
Second, as lack of a comparison group was a common reason for exclusion of studies from our review, researchers should be encouraged to adopt an appropriate observational design for future studies – ideally, a cohort design with at least one study group that includes people not exposed to the earthquake.
Third, given the breadth and potential complexity of many health-related outcomes, future surveillance should be planned using a centralised and multidisciplinary approach, including professionals such as epidemiologists, statisticians and public health professionals, to ensure the identification of appropriate study indicators and the development of efficient, standardised protocols that enable harmonised data collection and analysis.
Finally, future studies should make more regular use of routinely collected data, such as electronic health records, which would enable detailed assessment of earthquake effects in the long term.
Ripoll Gallardo A, Pacelli B, Alesina M, et al. Medium- and long-term health effects of earthquakes in high-income countries: a systematic review and meta-analysis. International Journal of Epidemiology, dyy130, https://doi.org/10.1093/ije/dyy130.
Alba Ripoll Gallardo is an academic anaesthetist and intensivist with experience working in various humanitarian settings. She is a postdoctoral fellow at CRIMEDIM (Research Center in Emergency and Disaster Medicine; a WHO Collaborating Centre) in Novara, Italy, and coordinates an international training program in humanitarian health developed in collaboration with Médecins Sans Frontières.
Barbara Pacelli is a biostatistician at the Regional Health and Social Care Agency of Emilia-Romagna, Bologna, Italy, and her research focuses on socio-environmental epidemiology.
Elias Allara is a public health doctor with training in epidemiology and medical statistics, currently studying towards a PhD in population health and genomics at the Department of Public Health and Primary Care, University of Cambridge, UK.
Cerebral palsy is the most common physical disability among children, with about two per 1000 live-born infants being diagnosed with the disorder. In most children with cerebral palsy, the disability is caused by damage to the immature brain during pregnancy or birth that results in problems with movement.
Denmark and Norway have low income inequality and free access to education and offer high-quality antenatal care to pregnant women free of charge. Nevertheless, in our study recently published in the International Journal of Epidemiology, we found that the risk of having a child with cerebral palsy in these two countries varies by the parents’ educational level, and this educational gradient has been surprisingly stable over time.
In our study, we aimed to assess whether the risk of having a child with cerebral palsy varied by different measures of parental socioeconomic status in Denmark and Norway. We found a strong educational gradient in the risk of having a child with cerebral palsy in both countries – the higher the education of the parents, the lower the risk. There was a one-third reduction in risk among those with a Bachelor or higher degree compared with parents with only primary or lower secondary education. Decreased risks of the same magnitude were found independently for both mothers and fathers, and these trends were stable over the past four decades, despite a large increase in the proportion of parents with higher education, especially among women.
The Nordic countries are known for their redistributive tax system and social policies aimed at reducing socioeconomic differences. The Nordic model has been successful in many respects – for example, Denmark and Norway rank as two of the OECD countries with the lowest income inequality. However, paradoxically, the social inequality in adverse health outcomes is larger than in many other European countries, and increasing.
In our study, we found no association between household income and the risk of having a child with cerebral palsy, when adjusting for parental education and age. Among parents-to-be in the Nordic setting, income may be a poorer marker of socioeconomic status – income has been more responsive to social policy, and parents are early in their careers when they have children. In addition, a higher income does not necessarily result in healthier behaviour.
A recent study reported a decreasing prevalence of cerebral palsy in Norway since 1999. The same has been found in a multicenter study in Europe. This positive trend is believed to be due to improvements in obstetric and neonatal care. Still, in a majority of children with cerebral palsy, the cause is unknown. It may be due to either genetic or environmental factors in pregnancy that cause damage to the brain before birth or increase the infant’s susceptibility to brain damage during or shortly after birth. It is important to continue research to identify causal factors for cerebral palsy in these children.
Our study suggests that risk factors that differ by socioeconomic status – such as maternal overweight, smoking, poor diet, maternal infections, paracetamol use and chronic disease – may play a role, and that there could be room for further prevention. Maternal overweight, smoking, genitourinary infections and paracetamol use have been linked to increased risk of cerebral palsy, while chronic disease and dietary factors have been less often investigated.
We also hypothesise that recurrence of cerebral palsy within families could partly explain our results: if cerebral palsy in parents affects their chance of undertaking higher education and increases the risk of having a child with cerebral palsy. We were not able to assess these potential underlying mechanisms in our study, but we hope to answer some of these questions in ongoing studies.
Forthun I, Strandberg-Larsen K, Wilcox AJ, et al. Parental socioeconomic status and risk of cerebral palsy in the child: evidence from two Nordic population-based cohorts. International Journal of Epidemiology, dyy139, https://doi.org/10.1093/ije/dyy139.
Ingeborg Forthun is an economist and PhD student at the Department of Global Public Health and Primary Care, University of Bergen, Norway.