Human birth seasonality: latitudinal gradient and interplay with childhood disease dynamics

An epidemiological study of season of birth, mental health, and neuroimaging in the UK Biobank

Environmental exposures during the perinatal period are known to have a long-term effect on adult physical and mental health. One such influential environmental exposure is the time of year of birth which affects the amount of daylight, nutrients, and viral load that an individual is exposed to within this key developmental period. Here, we investigate associations between season of birth (seasonality), four mental health traits (n = 137,588) and multi-modal neuroimaging measures (n = 33,212) within the UK Biobank. Summer births were associated with probable recurrent Major Depressive Disorder (β = 0.026, pcorr = 0.028) and greater mean cortical thickness in temporal and occipital lobes (β = 0.013 to 0.014, pcorr<0.05). Winter births were associated with greater white matter integrity globally, in the association fibers, thalamic radiations, and six individual tracts (β = -0.013 to -0.022, pcorr<0.05). Results of sensitivity analyses adjusting for birth weight were similar, with an additional association between winter birth and white matter microstructure in the forceps minor and between summer births, greater cingulate thickness and amygdala volume. Further analyses revealed associations between probable depressive phenotypes and a range of neuroimaging measures but a paucity of interactions with seasonality. Our results suggest that seasonality of birth may affect later-life brain structure and play a role in lifetime recurrent Major Depressive Disorder. Due to the small effect sizes observed, and the lack of associations with other mental health traits, further research is required to validate birth season effects in the context of different latitudes, and by co-examining genetic and epigenetic measures to reveal informative biological pathways.

Preterm and Early-Term Delivery After Heat Waves in 50 US Metropolitan Areas

Importance

Heat waves are increasing in frequency, intensity, and duration and may be acutely associated with pregnancy outcomes.

Objective

To examine changes in daily rates of preterm and early-term birth after heat waves in a 25-year nationwide study.

Design, Setting, and Participants

This cohort study of singleton births used birth records from 1993 to 2017 from the 50 most populous US metropolitan statistical areas (MSAs). The study included 53 million births, covering 52.8% of US births over the period. Data were analyzed between October 2022 and March 2023 at the National Center for Health Statistics.

Exposures

Daily temperature data from Daymet at 1-km2 resolution were averaged over each MSA using population weighting. Heat waves were defined in the 4 days (lag, 0-3 days) or 7 days (lag, 0-6 days) preceding birth.

Main Outcomes and Measures

Daily counts of preterm birth (28 to <37 weeks), early-term birth (37 to <39 weeks), and ongoing pregnancies in each gestational week on each day were enumerated in each MSA. Rate ratios for heat wave metrics were obtained from time-series models restricted to the warm season (May to September) adjusting for MSA, year, day of season, and day of week, and offset by pregnancies at risk.

Results

There were 53 154 816 eligible births in the 50 MSAs from 1993 to 2017; 2 153 609 preterm births and 5 795 313 early-term births occurring in the warm season were analyzed. A total of 30.0% of mothers were younger than 25 years, 53.8% were 25 to 34 years, and 16.3% were 35 years or older. Heat waves were positively associated with daily rates of preterm and early-term births, showing a dose-response association with heat wave duration and temperatures and stronger associations in the more acute 4-day window. After 4 consecutive days of mean temperatures exceeding the local 97.5th percentile, the rate ratio for preterm birth was 1.02 (95% CI, 1.00-1.03), and the rate ratio for early-term birth was 1.01 (95% CI, 1.01-1.02). For the same exposure, among those who were 29 years of age or younger, had a high school education or less, and belonged to a racial or ethnic minority group, the rate ratios were 1.04 (95% CI, 1.02-1.06) for preterm birth and 1.03 (95% CI, 1.02-1.05) for early-term birth. Results were robust to alternative heat wave definitions, excluding medically induced deliveries, and alternative statistical model specifications.

Conclusions and Relevance

In this cohort study, preterm and early-term birth rates increased after heat waves, particularly among socioeconomically disadvantaged subgroups. Extreme heat events have implications for perinatal health.

Risk, sanctions and norm change: the formation and decay of social distancing norms

Global challenges like the climate crisis and pandemic outbreaks require collective responses where people quickly adapt to changing circumstances. Social norms are potential solutions, but only if they themselves are flexible enough. The COVID-19 pandemic provided a unique opportunity to study norm formation and decay in real-world contexts. We tracked empirical and normative expectations about social distancing and empirical and normative expectations of sanctioning from June 2021 to February 2022 to explore how norms and meta norms evolved as COVID-19 risk decreased and increased. We found that norms and meta norms partially coevolve with risk dynamics, although they recover with some delay. This implies that norms should be enforced as soon as risk increases. We therefore tested how sanctioning intentions vary for different hypothetical norms and find them to increase with a clear meta norm of sanctioning, yet decrease with a clear social norm of distance. In conclusion, social norms evolve spontaneously with changing risk, but might not be adaptive enough when the lack of meta norms of sanctioning introduce tolerance for norm violations. Moreover, norm nudges can potentially have negative externalities if strengthening the social norm increases tolerance for norm violations. These results put some limits to social norms as solutions to guide behaviour under risk. This article is part of the theme issue 'Social norm change: drivers and consequences'.

Homo temporus: Seasonal Cycles as a Fundamental Source of Variation in Human Psychology

Many animal species exhibit seasonal changes in their physiology and behavior. Yet despite ample evidence that humans are also responsive to seasons, the impact of seasonal changes on human psychology is underappreciated relative to other sources of variation (e.g., personality, culture, development). This is unfortunate because seasonal variation has potentially profound conceptual, empirical, methodological, and practical implications. Here, we encourage a more systematic and comprehensive collective effort to document and understand the many ways in which seasons influence human psychology. We provide an illustrative summary of empirical evidence showing that seasons impact a wide range of affective, cognitive, and behavioral phenomena. We then articulate a conceptual framework that outlines a set of causal mechanisms through which seasons can influence human psychology-mechanisms that reflect seasonal changes not only in meteorological variables but also in ecological and sociocultural variables. This framework may be useful for integrating many different seasonal effects that have already been empirically documented and for generating new hypotheses about additional seasonal effects that have not yet received empirical attention. The article closes with a section that provides practical suggestions to facilitate greater appreciation for, and systematic study of, seasons as a fundamental source of variation in human psychology.

Studying the seasonality of conceptions among five distinct population subgroups in mainland Greece: a story of similarities and variability

The paper studies seasonality of conceptions among five distinct population subgroups of mainland Greece for the period 1951-2002. The populations explored include those residing in Metsovo, Dion, Organi, Kehros, as well as a "General" Sample consisting of persons located in various areas of continental Greece. The populations under investigation present diverse characteristics regarding religion, cultural background, socio-economic status etc. Records of births were derived from the Vital Registration System of the respective municipalities and communities of the populations under research were constructed. The date of child conception was estimated as the recorded date of birth minus 260 days.The analysis focuses, among others, on the construction of seasonal indices, applying a variant ratio to moving averages method which reveal, in relative terms, the seasonality of the phenomenon. Subsequently, these ratios are considered as the dependent variable in regression models while months, expressed in terms of dummy variables, are introduced as predictors. Four main sub-periods are considered; 1951-64, 1965-80, 1981-92 and 1992-2002. The findings show that the extent of seasonality differs between periods as well as between the five population subgroups though the phenomenon becomes less prominent over time in all cases. There is a tendency of an increased number of conceptions among mountainous populations during summer, irrespective of religion or socio-economic status, possibly partly due to environmental factors (i.e. seasonal workload, domestic organisation of extended families, etc). Nevertheless, the mountainous populations differ regarding the intensity and duration of this phenomenon. By contrast, in Dion, a lowland Christian Orthodox population, conceptions increase after Easter and remain elevated until June.

Mumps epidemic dynamics in the United States before vaccination (1923-1932)

Mumps is a vaccine-preventable, reemerging, and highly transmissible infectious disease. Widespread vaccination dramatically reduced cases; however, case counts have been increasing over the past 20 years. To provide a quantitative overview of historical mumps dynamics that can act as baseline information to help identify causes of mumps reemergence, we analyzed timeseries of cases reported from 1923 to 1932 in the United States. During that time, 239,230 mumps cases were reported in 70 cities. Larger cities reported annual epidemics and smaller cities reported intermittent, sporadic outbreaks. The critical community size above which transmission continuously occurred was likely between 365,583 and 781,188 individuals but could range as high as 3,376,438 individuals. Mumps cases increased as city size increased, suggesting density-dependent transmission. Using a density-dependent SEIR model, we calculated a mean effective reproductive number (Re) of 1.2. Re varied by city and over time, with periodic high values that could characterize short periods of very high transmission known as superspreading events. Case counts most often peaked in March, with higher-than-average transmission from December through April and showed a correlation with weekly births. While certain city pairs in Midwestern states had synchronous outbreaks, most outbreaks were less synchronous and not driven by distance between cities. This work demonstrates the importance of long-term infectious disease surveillance data and will inform future studies on mumps reemergence and control.

A multi-site study of the relationship between photoperiod and ovulation rate using Natural Cycles data

Many species exhibit seasonal patterns of breeding. Although humans can shield themselves from many season-related stressors, they appear to exhibit seasonal patterns of investment in reproductive function nonetheless, with levels of sex steroid hormones being highest during the spring and summer months. The current research builds on this work, examining the relationship between day length and ovarian function in two large samples of women using data from the Natural Cycles birth control application in each Sweden and the United States. We hypothesized that longer days would predict higher ovulation rates and sexual motivation. Results revealed that increasing day length duration predicts increased ovulation rate and sexual behavior, even while controlling for other relevant factors. Results suggest that day length may contribute to observed variance in women's ovarian function and sexual desire.

Signatures of geography, climate and foliage on given names of baby girls

Parents often weigh social, familial and cultural considerations when choosing their baby's name, but the name they choose could potentially be influenced by their physical or biotic environments. Here we examine whether the popularity of month and season names of girls covary geographically with environmental variables. In the continental USA, April, May and June (Autumn, Summer) are the most common month (season) names: April predominates in southern states (early springs), whereas June predominates in northern states (later springs). Whether April's popularity has increased with recent climate warming is ambiguous. Autumn is most popular in northern states, where autumn foliage is notably colourful, and in eastern states having high coverage of deciduous foliage. On a continental scale, Autumn was most popular in English-speaking countries with intense colouration of autumn foliage. These analyses are descriptive but indicate that climate and vegetation sometimes influence parental choice of their baby's name.

The influence of demographic and meteorological factors on temporal patterns of rotavirus infection in Dhaka, Bangladesh

To quantify the potential impact of rotavirus vaccines and identify strategies to improve vaccine performance in Bangladesh, a better understanding of the drivers of pre-vaccination rotavirus patterns is required. We developed and fitted mathematical models to 23 years (1990-2012) of weekly rotavirus surveillance data from Dhaka with and without incorporating long-term and seasonal variation in the birth rate and meteorological factors. We performed external model validation using data between 2013 and 2019 from the regions of Dhaka and Matlab. The models showed good agreement with the observed age distribution of rotavirus cases and captured the observed shift in seasonal patterns of rotavirus hospitalizations from biannual to annual peaks. The declining long-term trend in the birth rate in Bangladesh was the key driver of the observed shift from biannual to annual winter rotavirus patterns. Meteorological indices were also important: a 1°C, 1% and 1 mm increase in diurnal temperature range, surface water presence and degree of wetness were associated with a 19%, 3.9% and 0.6% increase in the transmission rate, respectively. The model demonstrated reasonable predictions for both Dhaka and Matlab, and can be used to evaluate the impact of rotavirus vaccination in Bangladesh against changing patterns of disease incidence.

Reproductive seasonality in the Baka Pygmies, environmental factors and climatic changes

Reproductive seasonality is a phenomenon common to human and animal populations and driven by, among others, climatic variables. Given the currently changing climate and its impacts on both the environment and human lives, the question arises of its potential effects on reproductive seasonality. Few studies have specifically explored the seasonality of reproduction among hunter-gatherers and anyone investigated how current climate change might affect this phenomenon. In this study we addressed reproductive seasonality in the Baka Pygmy living in African rain forests. Since reproductive seasonality can be linked to weather patterns, we explore this possibility. However, climatic variables driving weather patterns have changed over the years, so we assessed whether this has influenced the Baka reproductive pattern. Based on 34 years of written birth records and oral questionnaires from 13 years of systematic fieldwork, we observed a bimodal birth pattern with two birth peaks at 6-month intervals. Our results demonstrate that precipitation at conception or at birth potentially has effects, respectively negative and positive on the monthly number of births; and temperature has a role in controlling other variables that do affect the reproductive pattern. Changing weather patterns appear to be affecting the reproductive seasonality in the Baka, suggesting that attention needs to be given to the influence of global climate change on forager societies.

Impact of the Season of Birth on the Development of Juvenile Idiopathic Arthritis in the United States: A Nationwide Registry-based Study

OBJECTIVE

Autoimmune disorders result from the interplay of genetic and environmental factors. Many autoimmune disorders are associated with specific seasons of birth, implicating a role for environmental determinants in their etiopathology. We investigated if there is an association between the season of birth and the development of juvenile idiopathic arthritis ( JIA).

METHODS

Birth data from 10,913 children with JIA enrolled at 62 Childhood Arthritis and Rheumatology Research Alliance Registry sites was compared with 109,066,226 US births from the same period using a chi‑square goodness-of-fit test. Season of birth of the JIA cohort was compared to the US population estimate using a 2-sided 1-sample test for a binomial proportion and corrected for multiple comparisons. Secondary analysis was performed for JIA categories, age of onset, and month of birth.

RESULTS

A greater proportion of children with JIA were born in winter (January-March) compared to the US general population (25.72% vs 24.08%; corrected P < 0.0001). This observation was also true after stratifying for age of onset (≤ or > 6 yrs). When analyzed by the month of birth, a greater proportion of children with JIA were born in January compared to the US population (9.44% vs 8.13%; corrected P < 0.0001).

CONCLUSION

Relative to the general population, children with JIA are more often born in the winter, and specifically in the month of January. These observations support the hypothesis that seasonal variations in exposures during the gestational and/or early postnatal periods may contribute to development of JIA.

Seasonal patterns in fecundability in North America and Denmark: a preconception cohort study

STUDY QUESTION

To what extent does fecundability vary across seasons?

SUMMARY ANSWER

After accounting for seasonal patterns in pregnancy planning, we observed higher fecundability in the fall and lower fecundability in the spring, particularly at lower latitudes.

WHAT IS KNOWN ALREADY

In human populations, there are strong seasonal patterns of births that vary across geographic regions and time periods. However, previous studies of seasonality and fecundity are limited because they examine season of birth rather than season of conception and therefore neglect to account for seasonal variation in initiating attempts to conceive or pregnancy loss or differences in gestational length.

STUDY DESIGN, SIZE, DURATION

We conducted a preconception cohort study of 14 331 women residing in North America (June 2013-May 2018: n = 5827) and Denmark (June 2007-May 2018: n = 8504). Participants were attempting to conceive without fertility treatment and had been attempting pregnancy for ≤6 menstrual cycles at enrolment.

PARTICIPANTS/MATERIAL, SETTING, METHODS

We collected information on season of each pregnancy attempt using last menstrual period dates over the study period. Pregnancy was reported on female bi-monthly follow-up questionnaires. We fit log-binomial models with trigonometric regression to examine periodic variation in fecundability. We accounted for seasonal variation in initiation of pregnancy attempts by including indicator variables for menstrual cycle of attempt in the regression models.

MAIN RESULTS AND THE ROLE OF CHANCE

Initiation of pregnancy attempts peaked in September, with stronger seasonality in North America than in Denmark (48 vs. 16% higher probability initiating attempts in September compared with March). After accounting for seasonal variation in initiation of pregnancy attempts, we observed modest seasonal variation in fecundability, with a peak in the late fall and early winter in both cohorts, but stronger peak/low ratios in North America (1.16; 95% confidence interval [CI]: 1.05, 1.28) than in Denmark (1.08; 95% CI: 1.00, 1.16). When we stratified the North American data by latitude, we observed the strongest seasonal variation in the southern USA (peak/low ratio of 1.45 [95% CI: 1.14, 1.84]), with peak fecundability in late November.

LIMITATIONS, REASONS FOR CAUTION

We estimated menstrual cycle dates between follow-up questionnaires, which may have introduced exposure misclassification, particularly when women skipped follow-up questionnaires. We were unable to measure seasonally varying factors that may have influenced fecundability, including ambient temperature, vitamin D levels or infectious disease.

WIDER IMPLICATIONS OF THE FINDINGS

An understanding of how fecundability varies across seasons could help identify factors that can impair reproductive function. Neglecting to account for seasonal variation in initiation of pregnancy attempts could bias estimates of seasonal patterns in fecundability. This is the first preconception cohort study to examine seasonal variation in fecundability after accounting for seasonality in initiation of pregnancy attempts. Fecundability was highest in the fall and lowest in the spring, with stronger effects in southern latitudes of North America, suggesting that seasonal exposures may affect fecundity.

STUDY FUNDING/COMPETING INTEREST(S)

This research was funded by the Eunice K. Shriver National Institute of Child Health and Human Development (R21-050264, R01-HD060680, R21-HD072326 and R01-HD086742) and the Danish Medical Research Council (271-07-0338). The authors declare no conflicts of interest.

NDVI predicts birth seasonality in historical Baja California Sur, Mexico: adaptive responses to arid ecosystems and the North American Monsoon

Birth seasonality is a phenomenon whereby populations can be characterized by a single month or season in which births peak. While non-human animal research suggests that seasonal birth-pulses are related to variation in climate and local energy availability, social scientists debate the mechanisms responsible for it in humans. Here we investigate the role of precipitation, temperature, and energy availability on seasonal conception and birth pulses using a historical dataset from the Baja California peninsula - a hot, arid desert that experiences seasonal climatic fluctuations associated with the North American Monsoon. Analyses suggest that 1) local energy availability had a negative relationship with conception pulses; and 2) birth pulses had a positive relationship with local energy availability and a negative relationship with temperature. Taken together, our analyses suggest that women timed conceptions when local energy availability was lowest (challenging expectations of conception rates as simply reflecting ecological influences on female fecundity), so that children were born during the seasonal "green-up" associated with the North American Monsoon. Given our results, we speculate that birth seasonality represents a form of traditional ecological knowledge to improve neonate health and wellbeing.

The impact of past vaccination coverage and immunity on pertussis resurgence

The resurgence of pertussis over the past decades has resulted in incidence levels not witnessed in the United States since the 1950s. The underlying causes have been the subject of much speculation, with particular attention paid to the shortcomings of the latest generation of vaccines. We formulated transmission models comprising competing hypotheses regarding vaccine failure and challenged them to explain 16 years of highly resolved incidence data from Massachusetts, United States. Our results suggest that the resurgence of pertussis is a predictable consequence of incomplete historical coverage with an imperfect vaccine that confers slowly waning immunity. We found evidence that the vaccine itself is effective at reducing overall transmission, yet that routine vaccination alone would be insufficient for elimination of the disease. Our results indicated that the core transmission group is schoolchildren. Therefore, efforts aimed at curtailing transmission in the population at large, and especially in vulnerable infants, are more likely to succeed if targeted at schoolchildren, rather than adults.

Invariant predictions of epidemic patterns from radically different forms of seasonal forcing

Seasonal variation in environmental variables, and in rates of contact among individuals, are fundamental drivers of infectious disease dynamics. Unlike most periodically forced physical systems, for which the precise pattern of forcing is typically known, underlying patterns of seasonal variation in transmission rates can be estimated approximately at best, and only the period of forcing is accurately known. Yet solutions of epidemic models depend strongly on the forcing function, so dynamical predictions-such as changes in epidemic patterns that can be induced by demographic transitions or mass vaccination-are always subject to the objection that the underlying patterns of seasonality are poorly specified. Here, we demonstrate that the key bifurcations of the standard epidemic model are invariant to the shape of seasonal forcing if the amplitude of forcing is appropriately adjusted. Consequently, analyses applicable to real disease dynamics can be conducted with a smooth, idealized sinusoidal forcing function, and qualitative changes in epidemic patterns can be predicted without precise knowledge of the underlying forcing pattern. We find similar invariance in a seasonally forced predator-prey model, and conjecture that this phenomenon-and the associated robustness of predictions-might be a feature of many other periodically forced dynamical systems.

Panel Data Analysis via Mechanistic Models

Panel data, also known as longitudinal data, consist of a collection of time series. Each time series, which could itself be multivariate, comprises a sequence of measurements taken on a distinct unit. Mechanistic modeling involves writing down scientifically motivated equations describing the collection of dynamic systems giving rise to the observations on each unit. A defining characteristic of panel systems is that the dynamic interaction between units should be negligible. Panel models therefore consist of a collection of independent stochastic processes, generally linked through shared parameters while also having unit-specific parameters. To give the scientist flexibility in model specification, we are motivated to develop a framework for inference on panel data permitting the consideration of arbitrary nonlinear, partially observed panel models. We build on iterated filtering techniques that provide likelihood-based inference on nonlinear partially observed Markov process models for time series data. Our methodology depends on the latent Markov process only through simulation; this plug-and-play property ensures applicability to a large class of models. We demonstrate our methodology on a toy example and two epidemiological case studies. We address inferential and computational issues arising due to the combination of model complexity and dataset size. Supplementary materials for this article are available online.

Seasonality of births in horizontal strabismus: comparison with birth seasonality in schizophrenia and other disease conditions

Recent work has implicated one type of horizontal strabismus (exotropia) as a risk factor for schizophrenia. This new insight raises questions about a potential common developmental origin of the two diseases. Seasonality of births is well established for schizophrenia. Seasonal factors such as light exposure affect eye growth and can cause vision abnormalities, but little is known about seasonality of births in strabismus. We examined birth seasonality in people with horizontal strabismus in a retrospective study in Washoe County, Nevada, and re-examined similar previously obtained data from Osaka, Japan. We then compared seasonal patterns of births between strabismus, refractive error, schizophrenia and congenital toxoplasmosis. Patients with esotropia had a significant seasonality of births, with a deficit in March, then increasing to an excess in September, while patients with exotropia had a distinctly different pattern, with an excess of births in July, gradually decreasing to a deficit in November. These seasonalities were statistically significant with either χ2 or Kolmogorov-Smirnov-type statistics. The birth seasonality of esotropia resembled that for hyperopia, with an increase in amplitude, while the seasonality for myopia involved a phase-shift. There was no correlation between seasonality of births between strabismus and congenital toxoplasmosis. The pattern of an excess of summer births for people with exotropia was remarkably similar to the well-established birth seasonality of one schizophrenia subtype, the deficit syndrome, but not schizophrenia as a whole. This suggests a testable hypothesis: that exotropia may be a risk factor primarily for the deficit type of schizophrenia.

MERS-CoV as an emerging respiratory illness: A review of prevention methods

INTRODUCTION

Middle East Respiratory Coronavirus Virus (MERS-CoV) first emerged from Saudi Arabia in 2012 and has since been recognized as a significant human respiratory pathogen on a global level.

METHODS

In this narrative review, we focus on the prevention of MERS-CoV. We searched PubMed, Embase, Cochrane, Scopus, and Google Scholar, using the following terms: 'MERS', 'MERS-CoV', 'Middle East respiratory syndrome' in combination with 'prevention' or 'infection control'. We also reviewed the references of each article to further include other studies or reports not identified by the search.

RESULTS

As of Nov 2019, a total of 2468 laboratory-confirmed cases of MERS-CoV were diagnosed mostly from Middle Eastern regions with a mortality rate of at least 35%. A major outbreak that occurred outside the Middle East (in South Korea) and infections reported from 27 countries. MERS-CoV has gained recognition as a pathogen of global significance. Prevention of MERS-CoV infection is a global public health priority. Healthcare facility transmission and by extension community transmission, the main amplifier of persistent outbreaks, can be prevented through early identification and isolation of infected humans. While MERS-CoV vaccine studies were initially hindered by multiple challenges, recent vaccine development for MERS-CoV is showing promise.

CONCLUSIONS

The main factors leading to sustainability of MERS-CoV infection in high risk courtiers is healthcare facility transmission. MERS-CoV transmission in healthcare facility mainly results from laps in infection control measures and late isolation of suspected cases. Preventive measures for MERS-CoV include disease control in camels, prevention of camel to human transmission.

Project Tycho 2.0: a repository to improve the integration and reuse of data for global population health

Objective

In 2013, we released Project Tycho, an open-access database comprising 3.6 million counts of infectious disease cases and deaths reported for over a century by public health surveillance in the United States. Our objective is to describe how Project Tycho version 1 (v1) data has been used to create new knowledge and technology and to present improvements made in the newly released version 2.0 (v2).

Materials and Methods

We analyzed our user database and conducted online searches to analyze the use of Project Tycho v1 data. For v2, we added new US data and dengue data for other countries, and grouped data into 360 datasets, each with a digital object identifier and rich metadata. In addition, we used standard vocabularies to encode data where possible, improving compliance with FAIR (findable, accessible, interoperable, reusable) guiding principles for data management.

Results

Since release, 3174 people have registered to use Project Tycho data, leading to 18 new peer-reviewed papers and 27 other creative works, such as conference papers, student theses, and software applications. Project Tycho v2 comprises 5.7 million counts of infectious diseases in the United States and of dengue-related conditions in 98 additional countries.

Discussion

Project Tycho v2 contributes to improving FAIR compliance of global health data, but more work is needed to develop community-accepted standard representations for global health data.

Conclusion

FAIR principles are a valuable guide for improving the integration and reuse of data in global health to improve disease control and save lives.

Month-of-birth-effect in multiple sclerosis in Austria

BACKGROUND

The month-of-birth-effect (MoBE) describes the finding that multiple sclerosis (MS) patients seem to have been born significantly more frequently in spring, with a rise in May, and significantly less often in autumn and winter with the fewest births in November.

OBJECTIVES

To analyse if the MoBE can also be found in the Austrian MS population, and if so, whether the pattern is similar to the reported pattern in Canada, United Kingdom, and some Scandinavian countries.

METHODS

The data of 7886 MS patients in Austria were compared to all live births in Austria from 1940 to 2010, that is, 7.256545 data entries of the Austrian birth registry and analysed in detail.

RESULTS

Patterns observed in our MS cohort were not different from patterns in the general population, even when stratifying for gender. However, the noticeable and partly significant ups and downs over the examined years did not follow the distinct specific pattern with highest birth rates in spring and lowest birth rates in autumn that has been described previously for countries above the 49th latitude.

CONCLUSION

After correcting for month-of-birth patterns in the general Austrian population, there is no evidence for the previously described MoBE in Austrian MS patients.

Low Sun Exposure and Vitamin D Deficiency as Risk Factors for Inflammatory Bowel Disease, With a Focus on Childhood Onset

The incidence and prevalence of inflammatory bowel disease (IBD) are increasing worldwide. Some ecological studies show increasing incidence with increasing latitude. Ambient ultraviolet radiation varies inversely with latitude, and sun exposure of the skin is a major source of vitamin D. Vitamin D deficiency is common in patients with IBD. Sun exposure and vitamin D have immune effects that could plausibly reduce, or be protective for, IBD. One quarter of new IBD cases are diagnosed in childhood or adolescence, but most research is for adult-onset IBD. Here, we review the evidence for low sun exposure and/or vitamin D deficiency as risk factors for IBD, focusing where possible on pediatric IBD, where effects of environmental exposures may be clearer. The literature provides some evidence of a latitude gradient of IBD incidence, and evidence for seasonal patterns of timing of birth or disease onset is inconsistent. High prevalence of vitamin D deficiency occurs in people with IBD, but cannot be interpreted as being a causal risk factor. Evidence of vitamin D supplementation affecting disease activity is limited. Further research on predisease sun exposure and well-designed supplementation studies are required to elucidate whether these potentially modifiable exposures are indeed risk factors for IBD.

Wintertime stress, nursing, and lead exposure in Neanderthal children

Scholars endeavor to understand the relationship between human evolution and climate change. This is particularly germane for Neanderthals, who survived extreme Eurasian environmental variation and glaciations, mysteriously going extinct during a cool interglacial stage. Here, we integrate weekly records of climate, tooth growth, and metal exposure in two Neanderthals and one modern human from southeastern France. The Neanderthals inhabited cooler and more seasonal periods than the modern human, evincing childhood developmental stress during wintertime. In one instance, this stress may have included skeletal mobilization of elemental stores and weight loss; this individual was born in the spring and appears to have weaned 2.5 years later. Both Neanderthals were exposed to lead at least twice during the deep winter and/or early spring. This multidisciplinary approach elucidates direct relationships between ancient environments and hominin paleobiology.

Unintended consequences and the paradox of control: Management of emerging pathogens with age-specific virulence

We project forward total Zika virus disease (ZVD) under varying hazards of infection and consider how the age distribution of disease burden varies between these scenarios. Pathogens with age structured disease outcomes, such as rubella and Zika virus, require that management decisions consider their impact not only on total disease incidence but also on distribution of disease burden within a population. Some situations exhibit a "paradox of control" in which reductions of overall transmission decrease the total incidence but increase the incidence of severe disease. This happens because of corresponding increases in the average age of infection. Beginning with the current population structure and demographic rates of Brazil, we project forward total ZVD burden as measured by cases occurring in pregnant women and document the scenarios under which a paradox of control for ZVD management emerges. We conclude that while a paradox of control can occur for ZVD, the higher total costs from increasing the average age of infection will only be realized after several decades and vanish under conservative discounting of future costs. This indicates that managers faced with an emerging pathogen are justified to prioritize current disease incidence over potential increases in severe disease outcomes in the endemic state.

Season of birth and depression in adulthood: Revisiting historical forerunner evidence for in-utero effects

Evidence showing a relationship between season of birth and adult well-being is long-standing, but is now largely overlooked or dismissed. In light of increasingly compelling evidence for the effects of in-utero conditions on adult health, however, it is instructive to revisit the relationship, with an eye toward resolving the reasons for skepticism. This study uses data from the first National Health and Nutritional Examination Survey to examine the effects of month of birth on adult depression. The data correspond to an important time in history and the analysis points to one reason why enthusiasm for birth seasonality in depression has faded: although there was a strong relationship between month of birth and depression in the early 20th century, with spring and summer month births corresponding to significantly more depression, the relationship was largely eliminated by the 1940 birth cohort. Few adults alive today would be subject to this effect, but when it was apparent it was enormously consequential. Population attributable risk scenarios indicate that among those born between 1900 and 1920 the prevalence of major depression would have been reduced by approximately 22% if all births had been confined to November through March. The percent rises to 26% among those born between 1900 and 1910, and was likely even higher in earlier cohorts. Additional analyses point to the importance of nutritional deficits in explaining these effects. In the early 20th century, the relationship between month of birth and depression was weaker in circumstances where the food supply was less seasonally sensitive. For this reason, the turn-of-the-century relationship between month of birth and depression was much weaker among the well-educated, in Southern states, and in urban areas. Although birth seasonality in depression can be regarded as a historical artefact of diet and nutrition, evidence for its prior existence nonetheless speaks to the significance of other in-utero effects, both past and present.

MERS-CoV spillover at the camel-human interface

Middle East respiratory syndrome coronavirus (MERS-CoV) is a zoonotic virus from camels causing significant mortality and morbidity in humans in the Arabian Peninsula. The epidemiology of the virus remains poorly understood, and while case-based and seroepidemiological studies have been employed extensively throughout the epidemic, viral sequence data have not been utilised to their full potential. Here, we use existing MERS-CoV sequence data to explore its phylodynamics in two of its known major hosts, humans and camels. We employ structured coalescent models to show that long-term MERS-CoV evolution occurs exclusively in camels, whereas humans act as a transient, and ultimately terminal host. By analysing the distribution of human outbreak cluster sizes and zoonotic introduction times, we show that human outbreaks in the Arabian peninsula are driven by seasonally varying zoonotic transfer of viruses from camels. Without heretofore unseen evolution of host tropism, MERS-CoV is unlikely to become endemic in humans.

Geospatial characteristics of measles transmission in China during 2005-2014

Measles is a highly contagious and severe disease. Despite mass vaccination, it remains a leading cause of death in children in developing regions, killing 114,900 globally in 2014. In 2006, China committed to eliminating measles by 2012; to this end, the country enhanced its mandatory vaccination programs and achieved vaccination rates reported above 95% by 2008. However, in spite of these efforts, during the last 3 years (2013-2015) China documented 27,695, 52,656, and 42,874 confirmed measles cases. How measles manages to spread in China-the world's largest population-in the mass vaccination era remains poorly understood. To address this conundrum and provide insights for future public health efforts, we analyze the geospatial pattern of measles transmission across China during 2005-2014. We map measles incidence and incidence rates for each of the 344 cities in mainland China, identify the key socioeconomic and demographic features associated with high disease burden, and identify transmission clusters based on the synchrony of outbreak cycles. Using hierarchical cluster analysis, we identify 21 epidemic clusters, of which 12 were cross-regional. The cross-regional clusters included more underdeveloped cities with large numbers of emigrants than would be expected by chance (p = 0.011; bootstrap sampling), indicating that cities in these clusters were likely linked by internal worker migration in response to uneven economic development. In contrast, cities in regional clusters were more likely to have high rates of minorities and high natural growth rates than would be expected by chance (p = 0.074; bootstrap sampling). Our findings suggest that multiple highly connected foci of measles transmission coexist in China and that migrant workers likely facilitate the transmission of measles across regions. This complex connection renders eradication of measles challenging in China despite its high overall vaccination coverage. Future immunization programs should therefore target these transmission foci simultaneously.

Birth seasonality in rural areas of Iran, analysis of 5,536,262 births from 1992 to 2007

PURPOSE

We conducted this study to investigate birth seasonality in rural parts of Iran.

METHODS

In this study, patterns of 5,536,262 live births in rural parts of Iran between 1992 and 2007 were studied. Information about birth numbers, environmental factors, and sociocultural status of participants was obtained from previous works. Visually inspecting the seasonal variation of birth, studying its trend using autocorrelation analysis, examining the trend of birth seasonality using the seasonality coefficient, a newly introduced index, studying correlations between birth seasonality and possible associated factors, and analyzing associations between these variables and birth seasonality using multiple regression model were performed in this study.

RESULTS

In this study, we showed birth seasonality in rural parts of Iran, with the highest births in the first two seasons, winter and spring, mostly before the year of 2002. Latitude and mean temperature of districts, wealth status of families, education of women, and mothers' ages were associated with birth seasonality. However, latitude, temperature, and mothers' ages lost their associations after adjusting for sociocultural factors in the regression model.

CONCLUSIONS

Birth numbers in rural areas of Iran follow a rhythmic seasonal pattern; however, the ordering of seasons changes in the last years of the study period.

Disrupted seasonal biology impacts health, food security and ecosystems

The rhythm of life on earth is shaped by seasonal changes in the environment. Plants and animals show profound annual cycles in physiology, health, morphology, behaviour and demography in response to environmental cues. Seasonal biology impacts ecosystems and agriculture, with consequences for humans and biodiversity. Human populations show robust annual rhythms in health and well-being, and the birth month can have lasting effects that persist throughout life. This review emphasizes the need for a better understanding of seasonal biology against the backdrop of its rapidly progressing disruption through climate change, human lifestyles and other anthropogenic impact. Climate change is modifying annual rhythms to which numerous organisms have adapted, with potential consequences for industries relating to health, ecosystems and food security. Disconcertingly, human lifestyles under artificial conditions of eternal summer provide the most extreme example for disconnect from natural seasons, making humans vulnerable to increased morbidity and mortality. In this review, we introduce scenarios of seasonal disruption, highlight key aspects of seasonal biology and summarize from biomedical, anthropological, veterinary, agricultural and environmental perspectives the recent evidence for seasonal desynchronization between environmental factors and internal rhythms. Because annual rhythms are pervasive across biological systems, they provide a common framework for trans-disciplinary research.

Preventing Zika Virus Infection during Pregnancy Using a Seasonal Window of Opportunity for Conception

It has come to light that Zika virus (ZIKV) infection during pregnancy can result in trans-placental transmission to the fetus along with fetal death, congenital microcephaly, and/or Central Nervous System (CNS) malformations. There are projected to be >9,200,000 births annually in countries with ongoing ZIKV transmission. In response to the ZIKV threat, the World Health Organization (WHO) is strategically targeting prevention of infection in pregnant women and funding contraception in epidemic regions. I propose that the damaging effects of ZIKV can be reduced using a seasonal window of opportunity for conception that may minimize maternal exposure. Like other acute viral infections-including the related flavivirus, dengue virus (DENV)-the transmission of ZIKV is anticipated to be seasonal. By seasonally planning pregnancy, this aspect of pathogen ecology can be leveraged to align sensitive periods of gestation with the low-transmission season.

Evolution and Use of Dynamic Transmission Models for Measles and Rubella Risk and Policy Analysis

The devastation caused by periodic measles outbreaks motivated efforts over more than a century to mathematically model measles disease and transmission. Following the identification of rubella, which similarly presents with fever and rash and causes congenital rubella syndrome (CRS) in infants born to women first infected with rubella early in pregnancy, modelers also began to characterize rubella disease and transmission. Despite the relatively large literature, no comprehensive review to date provides an overview of dynamic transmission models for measles and rubella developed to support risk and policy analysis. This systematic review of the literature identifies quantitative measles and/or rubella dynamic transmission models and characterizes key insights relevant for prospective modeling efforts. Overall, measles and rubella represent some of the relatively simplest viruses to model due to their ability to impact only humans and the apparent life-long immunity that follows survival of infection and/or protection by vaccination, although complexities arise due to maternal antibodies and heterogeneity in mixing and some models considered potential waning immunity and reinfection. This review finds significant underreporting of measles and rubella infections and widespread recognition of the importance of achieving and maintaining high population immunity to stop and prevent measles and rubella transmission. The significantly lower transmissibility of rubella compared to measles implies that all countries could eliminate rubella and CRS by using combination of measles- and rubella-containing vaccines (MRCVs) as they strive to meet regional measles elimination goals, which leads to the recommendation of changing the formulation of national measles-containing vaccines from measles only to MRCV as the standard of care.

Seasonality and the effectiveness of mass vaccination

Many infectious diseases have seasonal outbreaks, which may be driven by cyclical environmental conditions (e.g., an annual rainy season) or human behavior (e.g., school calendars or seasonal migration). If a pathogen is only transmissible for a limited period of time each year, then seasonal outbreaks could infect fewer individuals than expected given the pathogen's in-season transmissibility. Influenza, with its short serial interval and long season, probably spreads throughout a population until a substantial fraction of susceptible individuals are infected. Dengue, with a long serial interval and shorter season, may be constrained by its short transmission season rather than the depletion of susceptibles. Using mathematical modeling, we show that mass vaccination is most efficient, in terms of infections prevented per vaccine administered, at high levels of coverage for pathogens that have relatively long epidemic seasons, like influenza, and at low levels of coverage for pathogens with short epidemic seasons, like dengue. Therefore, the length of a pathogen's epidemic season may need to be considered when evaluating the costs and benefits of vaccination programs.

Effect of vaccination programmes on mortality burden among children and young adults in the Netherlands during the 20th century: a historical analysis

BACKGROUND

In the 20th century, childhood mortality decreased rapidly, and vaccination programmes are frequently suggested as a contributing factor. However, quantification of this contribution is subject to debate or absent. We present historical data from the Netherlands that allow us to quantify the reduction in childhood mortality burden for vaccine-preventable diseases in this period as a function of vaccination coverage.

METHODS

We retrieved cause-specific and age-specific historical mortality data from Statistics Netherlands from 1903 to 2012 (for Dutch birth cohorts born from 1903 to 1992), and data for vaccination coverage since the start of vaccination programmes from the Dutch Health Care Inspectorate and the Dutch National Institute for Public Health and the Environment. We also obtained birth and migration data from Statistics Netherlands. We used a restricted mean life-time method to estimate cause-specific mortality burden among children and young adults for each birth cohort as the years of life lost up to age 20 years, excluding migration as a variable because this did not affect the results. To correct for long-term trends, we calculated the cause-specific contribution to the total childhood mortality burden.

FINDINGS

In the prevaccination era, the contribution to mortality burden was fairly constant for diphtheria (1·4%), pertussis (3·8%), and tetanus (0·1%). Around the start of mass vaccinations, these contributions to the mortality burden decreased rapidly to near zero. We noted similar patterns for poliomyelitis, mumps, and rubella. The number of deaths due to measles around the start of vaccination in the Netherlands were too few to detect an accelerated rate of decrease after mass vaccinations were started. We estimate that mass vaccination programmes averted 148 000 years of life lost up to age 20 years (95% prediction interval 110 000-201 000) among children born before 1992. This corresponds to about 9000 deaths averted (6000-12 000).

INTERPRETATION

Our historical time series analysis of mortality and vaccination coverage shows a strong association between increasing vaccination coverage and diminishing contribution of vaccine-preventable diseases to overall mortality. This analysis provides further evidence that mass vaccination programmes contributed to lowering childhood mortality burden.

FUNDING

Dutch Ministry of Health, Welfare and Sport.

The determinant of periodicity in Mycoplasma pneumoniae incidence: an insight from mathematical modelling

Until the early 1990 s, incidences of Mycoplasma pneumoniae (MP) infection showed three to five year epidemic cycles in multiple countries, however, the mechanism for the MP epidemic cycle has not been understood. Here, we investigate the determinant of periodicity in MP incidence by employing a mathematical model describing MP transmission dynamics. Three candidates for the determinant of periodicity were evaluated: school-term forcing, minor variance in the duration of immunity, and epidemiological interference between MP serotypes. We find that minor variation in the duration of immunity at the population level must be considered essential for the MP epidemic cycle because the MP cyclic incidence pattern did not replicate without it. Minor variation, in this case, is a less dispersed distribution for the duration of immunity than an exponential distribution. Various lengths of epidemic cycles, including cycles typically found in nature, e.g. three to five year cycles, were also observed when there was minor variance in the duration of immunity. The cyclic incidence pattern is robust even if there is epidemiological interference due to cross-immune protection, which is observed in the epidemiological data as negative correlation between epidemics per MP serotype.

Quantifying seasonal population fluxes driving rubella transmission dynamics using mobile phone data

Changing patterns of human aggregation are thought to drive annual and multiannual outbreaks of infectious diseases, but the paucity of data about travel behavior and population flux over time has made this idea difficult to test quantitatively. Current measures of human mobility, especially in low-income settings, are often static, relying on approximate travel times, road networks, or cross-sectional surveys. Mobile phone data provide a unique source of information about human travel, but the power of these data to describe epidemiologically relevant changes in population density remains unclear. Here we quantify seasonal travel patterns using mobile phone data from nearly 15 million anonymous subscribers in Kenya. Using a rich data source of rubella incidence, we show that patterns of population travel (fluxes) inferred from mobile phone data are predictive of disease transmission and improve significantly on standard school term time and weather covariates. Further, combining seasonal and spatial data on travel from mobile phone data allows us to characterize seasonal fluctuations in risk across Kenya and produce dynamic importation risk maps for rubella. Mobile phone data therefore offer a valuable previously unidentified source of data for measuring key drivers of seasonal epidemics.

Unraveling the Transmission Ecology of Polio

Sustained and coordinated vaccination efforts have brought polio eradication within reach. Anticipating the eradication of wild poliovirus (WPV) and the subsequent challenges in preventing its re-emergence, we look to the past to identify why polio rose to epidemic levels in the mid-20th century, and how WPV persisted over large geographic scales. We analyzed an extensive epidemiological dataset, spanning the 1930s to the 1950s and spatially replicated across each state in the United States, to glean insight into the drivers of polio’s historical expansion and the ecological mode of its persistence prior to vaccine introduction. We document a latitudinal gradient in polio’s seasonality. Additionally, we fitted and validated mechanistic transmission models to data from each US state independently. The fitted models revealed that: (1) polio persistence was the product of a dynamic mosaic of source and sink populations; (2) geographic heterogeneity of seasonal transmission conditions account for the latitudinal structure of polio epidemics; (3) contrary to the prevailing “disease of development” hypothesis, our analyses demonstrate that polio’s historical expansion was straightforwardly explained by demographic trends rather than improvements in sanitation and hygiene; and (4) the absence of clinical disease is not a reliable indicator of polio transmission, because widespread polio transmission was likely in the multiyear absence of clinical disease. As the world edges closer to global polio eradication and continues the strategic withdrawal of the Oral Polio Vaccine (OPV), the regular identification of, and rapid response to, these silent chains of transmission is of the utmost importance.

Using models to reveal the epidemiology of historic poliovirus transmission in the US, this study reconstructs the millions of silent infections and identifies why polio epidemics are explosive, seasonal, and vary geographically.

Thanks to global vaccination efforts, poliovirus is on the brink of worldwide eradication. However, achieving eradication and preventing re-emergence requires intimate knowledge of how the virus persists. In order to understand a system that is complicated by heavy human intervention, such as vaccination, it is important to establish a baseline by studying that system in the absence of intervention. Historical epidemics that predate the use of vaccines can be used to disentangle the epidemiology of disease from vaccine effects. Using historical polio data from large-scale epidemics in the US, we fitted and simulated mathematical models to track poliovirus and to reconstruct the millions of unobserved subclinical infections that propagated the disease. We identified why polio epidemics are explosive and seasonal, and why they vary geographically. Our analyses show that the historical expansion of polio is straightforwardly explained by the demographic “baby boom” during the postwar period rather than improvements in hygiene. We were also able to demonstrate that poliovirus persisted primarily through symptomless individuals, and that in the event of local virus extinction, infection was reintroduced from other geographic locations.

Dynamics of Pertussis Transmission in the United States

Past patterns of infectious disease transmission set the stage on which modern epidemiologic dynamics are played out. Here, we present a comprehensive account of pertussis (whooping cough) transmission in the United States during the early vaccine era. We analyzed recently digitized weekly incidence records from Morbidity and Mortality Weekly Reports from 1938 to 1955, when the whole-cell pertussis vaccine was rolled out, and related them to contemporary patterns of transmission and resurgence documented in monthly incidence data from the National Notifiable Diseases Surveillance System. We found that, during the early vaccine era, pertussis epidemics in US states could be categorized as 1) annual, 2) initially annual and later multiennial, or 3) multiennial. States with predominantly annual cycles tended to have higher per capita birth rates, more household crowding, more children per family, and lower rates of school attendance than the states with multiennial cycles. Additionally, states that exhibited annual epidemics during 1938-1955 have had the highest recent (2001-2010) incidence, while those states that transitioned from annual cycles to multiennial cycles have had relatively low recent incidence. Our study provides an extensive picture of pertussis epidemiology in the United States dating back to the onset of vaccination, a back-story that could aid epidemiologists in understanding contemporary transmission patterns.

Effect of religious rules on time of conception in Romania from 1905 to 2001

STUDY QUESTION

Does the interdiction of sexual intercourse during Nativity and Lent fasting periods have any effect on when babies are conceived in Romania, in the 20th century?

SUMMARY ANSWER

Based on date of birth records from the 20th century, Lent had a greater effect than the Nativity fast on conception within the Eastern Orthodox (ORTHD) population.

WHAT IS KNOWN ALREADY

Seasonality of births (and therefore of conception) is affected by geographical factors (latitude, weather, day-length). Other demographic, economic and socio-cultural characteristics (education, ethnicity, religion) have been proved to have an influence on conception.

STUDY DESIGN, SIZE, DURATION

The analyzed data consists of registered daily birth records for a long time series (35 429 points = 365 (days/year) × 97 years + 24 leap years), with 24 947 061 births in Romania over the period 1905-2001. The data were obtained from the 1992 and 2002 censuses.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Based on the reported birth date of each person, the estimated date of conception is computed using a standard gestation period of 280 days. The population was grouped into two categories (ORTHD and Non-Orthodox (NORTHD)) based on religious affiliation. Data analysis is performed in the same manner for both groups. Preliminary data analyses regarding seasonal variations in conception are considered first. Econometric models are applied and tested. The dependent variable in these models is the calculated date of conception, while the independent variables are: (i) religious affiliation; (ii) dates of Nativity and Lent fasts (the latter varies slightly from year to year); (iii) rural versus urban residence; (iv) length of day-light; (v) non-working days and (vi) trend. The models are tested for validity using analysis of variance while the regression coefficients are tested by the Student t-test.

MAIN RESULTS AND THE ROLE OF CHANCE

All models are statistically valid (P < 0.01); all regression coefficients for the ORTHD group are valid (P < 0.01, except for rurality between 1990 and 2001, with P < 0.05). The data analysis indicates smaller standard error bars on the parameters for the ORTHD group as compared with the NORTHD group. The conclusion is that religious affiliation is an important factor in date of conception.

LIMITATIONS, REASONS FOR CAUTION

The data do not refer to all births during the analyzed period, but only to those persons still alive at the 1992 and 2002 censuses. The date of conception was estimated assuming 280 days for gestation, which is a medically accepted time interval but will undoubtedly vary. However, the primary independent variables (Lent and Nativity fast at 48 and 40 days, respectively) are long enough to overlap the uncertainty in the conception date following the sexual intercourse event. We also must assume that the religious affiliation of the parents is well defined, based on the information given by their offspring at census time, and is the same for both parents.

WIDER IMPLICATIONS OF THE FINDINGS

Our findings are consistent with other studies, which show differences between religious groups on date of conception, although we reach different conclusions regarding the influence of weather on fertility in Romania.

STUDY FUNDING/COMPETING INTERESTS

B.V.I., M.A. and G.R. have no competing interests to declare. There is no connection to the current paper, but C.H. declares that (i) he is currently conducting a research titled 'Chronic Diseases' Direct Costs within the Romanian Health System' funded by Local American Working Group; (ii) his wife is employed to a Romanian company (A&D Pharma) that does business in the pharmaceutical sector. This paper is a part of G.R. and M.A. scientific activities in COST Action TD1210. This work by C.H. was co-financed by the European Social Fund through project number POSDRU/1.5/S/59184.

A century of transitions in New York City's measles dynamics

Infectious diseases spreading in a human population occasionally exhibit sudden transitions in their qualitative dynamics. Previous work has successfully predicted such transitions in New York City's historical measles incidence using the seasonally forced susceptible-infectious-recovered (SIR) model. This work relied on a dataset spanning 45 years (1928-1973), which we have extended to 93 years (1891-1984). We identify additional dynamical transitions in the longer dataset and successfully explain them by analysing attractors and transients of the same mechanistic epidemiological model.

Host and pathogen ecology drive the seasonal dynamics of a fungal disease, white-nose syndrome

Seasonal patterns in pathogen transmission can influence the impact of disease on populations and the speed of spatial spread. Increases in host contact rates or births drive seasonal epidemics in some systems, but other factors may occasionally override these influences. White-nose syndrome, caused by the emerging fungal pathogen Pseudogymnoascus destructans, is spreading across North America and threatens several bat species with extinction. We examined patterns and drivers of seasonal transmission of P. destructans by measuring infection prevalence and pathogen loads in six bat species at 30 sites across the eastern United States. Bats became transiently infected in autumn, and transmission spiked in early winter when bats began hibernating. Nearly all bats in six species became infected by late winter when infection intensity peaked. In summer, despite high contact rates and a birth pulse, most bats cleared infections and prevalence dropped to zero. These data suggest the dominant driver of seasonal transmission dynamics was a change in host physiology, specifically hibernation. Our study is the first, to the best of our knowledge, to describe the seasonality of transmission in this emerging wildlife disease. The timing of infection and fungal growth resulted in maximal population impacts, but only moderate rates of spatial spread.