Non-stationary dynamics of climate variability in synchronous influenza epidemics in Japan

Climate and human health: a review of publication trends in the International Journal of Biometeorology

The climate-health nexus is well documented in the field of biometeorology. Since its inception, Biometeorology has in many ways become the umbrella under which much of this collaborative research has been conducted. Whilst a range of review papers have considered the development of biometeorological research and its coverage in this journal, and a few have reviewed the literature on specific diseases, none have focused on the sub-field of climate and health as a whole. Since its first issue in 1957, the International Journal of Biometeorology has published a total of 2183 papers that broadly consider human health and its relationship with climate. In this review, we identify a total of 180 (8.3%, n = 2183) of these papers that specifically focus on the intersection between meteorological variables and specific, named diagnosable diseases, and explore the publication trends thereof. The number of publications on climate and health in the journal increases considerably since 2011. The largest number of publications on the topic was in 2017 (18) followed by 2021 (17). Of the 180 studies conducted, respiratory diseases accounted for 37.2% of the publications, cardiovascular disease 17%, and cerebrovascular disease 11.1%. The literature on climate and health in the journal is dominated by studies from the global North, with a particular focus on Asia and Europe. Only 2.2% and 8.3% of these studies explore empirical evidence from the African continent and South America respectively. These findings highlight the importance of continued research on climate and human health, especially in low- and lower-middle-income countries, the populations of which are more vulnerable to climate-sensitive illnesses.

Extreme influenza epidemics and out-of-hospital cardiac arrest

INTRODUCTION

There is compelling evidence for an association between influenza epidemics and major adverse cardiovascular events. However, the role of extreme influenza epidemics as a trigger of out-of-hospital cardiac arrest (OHCA) is unclear. Thus, we evaluated the potential association between extreme influenza epidemics and incidence of OHCA.

METHODS

We used a quasi-experimental design with time-series analysis of national registry data for cases of OHCA from all 47 prefectures of Japan during influenza seasons between 2005 and 2014. A Poisson regression time-series model with a distributed lag non-linear model was used to estimate prefecture-specific effects of influenza epidemics on OHCA. A multivariate meta-analysis was conducted for nationally pooled estimates.

RESULTS

In total, 481,516 OHCAs of presumed cardiac origin were reported during the study period. The minimum morbidity percentile (MMP) was estimated as the 0th percentile for influenza incidence. The overall cumulative relative risk versus the MMP was 1.25 (95% confidence interval, 1.16-1.34) for extreme influenza epidemics (at the 99th percentile of influenza incidence). The effect of extreme influenza epidemics was significant for lag periods of 1.5-7.1 and 17.9-21 days. Multivariate random-effects meta-analysis indicated significant spatial heterogeneity among prefectures (Cochran Q test, p = 0.011; I² = 23.2%).

CONCLUSION

Extreme influenza epidemics are associated with higher risk of OHCA. Our findings suggest that several weeks' prevention for extreme influenza infections should be implemented to reduce the risk of OHCA.

Out-of-Hospital Cardiac Arrests During the Japanese Professional Baseball Championship Series

Because the Japan Professional Baseball Championship Series (Japan Series) is a stressful sports event, it is possible that watching Japan Series matches may increase the risk of cardiovascular events. Therefore, we investigated the potential association between the Japan Series and the incidence of out-of-hospital cardiac arrest (OHCA) events. National registry data for all cases of OHCA between 2005 and 2014 from 47 prefectures of Japan were obtained. We used a time-stratified case-crossover design with a conditional Poisson regression model to compare OHCA events during the Japan Series with those events that occurred during the periods except for dates of the Japan Series. The estimated associations for each prefecture were pooled at the nationwide level using a random-effects meta-analysis. In total, 666,020 OHCAs of presumed cardiac origin were reported during the study period. On days of Japan Series matches, the pooled relative risk of OHCA was 1.033 (95% confidence interval 1.012 to 1.055; p = 0.002; I² = 3.5%, P for heterogeneity = 0.405). Stratified analyses by gender revealed that the substantial increase in OHCA during the events was observed for men, whereas we found no significant increase for women. We also found a considerable rise in OHCA among patients aged ≥65 years; however, there was no significant evidence of increased risk in those aged 18 to 64 years. In conclusion, stressful baseball match is associated with an increased risk of OHCA. Prevention measures for severe emotional stress-related OHCA should be implemented, particularly for elderly men.

Different responses of influenza epidemic to weather factors among Shanghai, Hong Kong, and British Columbia

Weather factors have long been considered as key sources for regional heterogeneity of influenza seasonal patterns. As influenza peaks coincide with both high and low temperature in subtropical cities, weather factors may nonlinearly or interactively affect influenza activity. This study aims to assess the nonlinear and interactive effects of weather factors with influenza activity and compare the responses of influenza epidemic to weather factors in two subtropical regions of southern China (Shanghai and Hong Kong) and one temperate province of Canada (British Columbia). Weekly data on influenza activity and weather factors (i.e., mean temperature and relative humidity (RH)) were obtained from pertinent government departments for the three regions. Absolute humidity (AH) was measured by vapor pressure (VP), which could be converted from temperature and RH. Generalized additive models were used to assess the exposure-response relationship between weather factors and influenza virus activity. Interactions of weather factors were further assessed by bivariate response models and stratification analyses. The exposure-response curves of temperature and VP, but not RH, were consistent among three regions/cities. Bivariate response model revealed a significant interactive effect between temperature (or VP) and RH (P < 0.05). Influenza peaked at low temperature or high temperature with high RH. Temperature and VP are important weather factors in developing a universal model to explain seasonal outbreaks of influenza. However, further research is needed to assess the association between weather factors and influenza activity in a wider context of social and environmental conditions.