Short-term effects of heat on respiratory mortality and morbidity in Germany – small-area analysis in the framework of the EXHAUSTION project

Abstract

Background and Aim: Short-term associations between heat and respiratory mortality and morbidity have been well recognized. However, most studies were conducted in major cities, whereas evidence for more rural areas is limited. In this study, we assessed the short-term associations between air temperature and cause-specific respiratory mortality and hospital admissions in the warm season (May-September) in Germany at a small-area level. Methods: Daily counts of mortality and hospital admissions for respiratory diseases, chronic obstructive pulmonary disease, asthma, lower respiratory tract infections, and pneumonia from 2000 to 2016 were obtained for Germany at the small-area level. Small areas were defined as districts for mortality data and municipalities for hospital admission data. Daily mean air temperatures estimated by a spatio-temporal model were assigned to each small area. We first applied small area-specific Poisson regression allowing for overdispersion, using Distributed Lag Non-linear Models to assess the heat effects at lag 0-1 days (average of same- and previous-day temperatures). Random-effects meta-analysis was then used to pool the small area-specific estimates. Besides, we conducted subgroup analyses to investigate effect modification by age and sex. Results: We observed increased risks for all investigated cause-specific respiratory mortality and hospital admissions associated with heat. The strongest heat effect was found for pneumonia. For an increment from the 75th to the 99th percentile of the temperature distribution, the pooled risk ratio was 1.49 (95% CI: 1.42, 1.57) for pneumonia mortality and 1.20 (95% CI: 1.19, 1.22) for pneumonia hospital admissions. The heat effects were stronger among the elderly (75+ years) and females. Conclusions: Using data from both urban and rural areas, our study suggests the adverse heat effects on respiratory mortality and morbidity in the warm season in Germany. These heat effects were more pronounced among the elderly and females. Keywords: Air temperature, heat, respiratory, mortality, hospital admissions