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High Temperature and Hospitalizations for Cardiovascular and Respiratory Causes in 12 European Cities

¹ Department of Epidemiology, Local Health Authority Rome E, Rome, Italy; ² Biostatistics Unit, Institute for Cancer Prevention (ISPO), Florence, Italy; ³ Department of Statistics, University of Florence, Italy; ⁴ Division of Community Health Sciences, St. George's, University of London, London, United Kingdom; ⁵ Department of Hygiene and Epidemiology, Medical School, University of Athens, Athens, Greece; ⁶ Valencia School of Health Studies, Valencia, Spain; ⁷ Department of Epidemiology, Health Authority Milan, Milan, Italy; ⁸ Regional Environmental Protection Agency of Piedmont, Grugliasco, Italy; ⁹ Department of Environmental Health, Umeå University, Umeå, Sweden; ¹⁰ St. James's Hospital, Dublin, Ireland; ¹¹ Department of Environmental Health, Institute of Public Health, Ljubljana, Slovenia; ¹² Departement Santé-Environnement, Institut de Veille Sanitaire, Bordeaux, France; ¹³ Department of Biology, Jozsef Fodor National Center of Public Health, Budapest, Hungary; ¹⁴ Institute of Social and Preventive Medicine of the University of Basel, Basel, Switzerland; and ¹⁵ Municipal Medical Research Institute, Barcelona, Spain

Correspondence and requests for reprints should be addressed to Dr. Paola Michelozzi, Department of Epidemiology Local Health Authority RM/E, Via di Santa Costanza 53, 00198 Rome, Italy. E-mail: michelozzi{at}asplazio.it

Rationale: Episode analyses of heat waves have documented a comparatively higher impact on mortality than on morbidity (hospital admissions) in European cities. The evidence from daily time series studies is scarce and inconsistent.

Objectives: To evaluate the impact of high environmental temperatures on hospital admissions during April to September in 12 European cities participating in the Assessment and Prevention of Acute Health Effects of Weather Conditions in Europe (PHEWE) project.

Methods: For each city, time series analysis was used to model the relationship between maximum apparent temperature (lag 0–3 days) and daily hospital admissions for cardiovascular, cerebrovascular, and respiratory causes by age (all ages, 65–74 age group, and 75+ age group), and the city-specific estimates were pooled for two geographical groupings of cities.

Measurements and Main Results: For respiratory admissions, there was a positive association that was heterogeneous between cities. For a 1°C increase in maximum apparent temperature above a threshold, respiratory admissions increased by +4.5% (95% confidence interval, 1.9–7.3) and +3.1% (95% confidence interval, 0.8–5.5) in the 75+ age group in Mediterranean and North-Continental cities, respectively. In contrast, the association between temperature and cardiovascular and cerebrovascular admissions tended to be negative and did not reach statistical significance.

Conclusions: High temperatures have a specific impact on respiratory admissions, particularly in the elderly population, but the underlying mechanisms are poorly understood. Why high temperature increases cardiovascular mortality but not cardiovascular admissions is also unclear. The impact of extreme heat events on respiratory admissions is expected to increase in European cities as a result of global warming and progressive population aging.

Key Words: heat • hospital admissions • elderly • respiratory diseases • cardiovascular diseases

AT A GLANCE COMMENTARY Scientific Knowledge on the Subject It is known that high temperatures increase mortality from cardiovascular and respiratory causes, but there is limited information about the effects of high temperatures on morbidity. What This Study Adds to the Field High temperatures increase the risk of hospitalization for respiratory diseases, with geographical heterogeneity. Although previous research showed that high temperatures increase cardiovascular mortality, this was not observed for admissions.