Mortality has been shown to increase with extremely hot ambient temperatures. Details on the specific cause of mortality can be useful for improving preventive policies. Infants are often identified as a population that is vulnerable to extreme heat conditions; however, information on heat and infant mortality is scarce, with no studies reporting on cause-specific mortality.
The study includes all deaths in the Catalonia region of Spain during the warm seasons of 1983–2006 (503,389 deaths). We used the case-crossover design to evaluate the association between the occurrence of extremely hot days (days with maximum temperature above the 95th percentile) and mortality. Total mortality and infant mortality were stratified into 66 and 8 causes of death, respectively.
Three consecutive hot days increased total daily mortality by 19%. We calculated that 1.6% of all deaths were attributable to heat. About 40% of attributable deaths did not occur during heat-wave periods. The causes of death that were increased included cardiovascular and respiratory diseases, mental and nervous system disorders, infectious and digestive system diseases, diabetes, and some external causes such as suicide. In infants, the effect of heat was observed on the same day and was detected only for conditions originating in the perinatal period (relative risk = 1.53 [95% confidence interval = 1.16–2.02]). Within the perinatal causes, cardiovascular, respiratory, digestive system, and hemorrhagic and hematologic disorders were the causes of death with stronger effects.
Heat contributes to an increase in mortality from several causes. In infants, the first week of life is the most critical window of vulnerability.
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From the aCentre for Research in Environmental Epidemiology (CREAL), Barcelona, Spain; bMunicipal Institute of Medical Research (IMIM-Hospital del Mar), Barcelona, Spain; cCIBER Epidemiología y Salud Pública (CIBERESP), Barcelona, Spain; dServei Meteorològic de Catalunya, Barcelona, Spain; eAir Pollution Epidemiology Section, California Office of Environmental Health Hazard Assessment, Oakland, CA; and fDepartment of Experimental and Health Sciences, Universitat Pompeu Fabra, Barcelona, Spain. C.S. and J.B.-G. contributed equally to this manuscript.
Submitted 10 December 2010; accepted 2 June 2011.
Conflicts of interest and sources of funding: Medina-Ramón received funding from the Spanish Ministry of Science and Innovation through the Programme Juan de la Cierva (JCI-2007–47–767). Study funded in part by Agència de Gestió d'Ajuts Universitaris i de Recerca (AGAUR) (grant 2009 SGR 501). The other authors reported no financial interests related to this research.
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Correspondence: Xavier Basagaña, Centre for Research in Environmental Epidemiology (CREAL), Doctor Aiguader 88, 08003 Barcelona, Catalonia, Spain. E-mail: firstname.lastname@example.org.