The effect of air-conditioning (AC) on the in hospital mortality during the 2003 heat-wave in Mainland Portugal

Abstract

The August 2003 heat-wave accounted for an excess of more than 1900 deaths in Portugal. At the European level it is acknowledged that this heat-wave was responsible for an excess of about 70000 deaths. In both situations a considerable number of deaths seem to have occurred in hospitals. The aim of this study was to evaluate the association between hospital existence of AC and the in hospital mortality rate during the 2003 heat-wave in Portugal mainland. A historic cohort design was used, including all patients with aged 45 or more, hospitalized during the last 7 days before the beginning of 2003’s heat-wave, and, therefore exposed to excess heat only in hospital. The study endpoint was the survival of patients in the 18 days of the heat-wave plus two days. This endpoint was compared between patients in services with air-conditioning (AC+) against patients in services without air-conditioning (AC-). Data was obtained from the National Hospital Discharge Database. Information on the air-conditioning existence was obtained by a survey of hospital administrations during 2007. The association between the survival of patients and being hospitalized in AC+ services was assessed with a Cox regression model that has included the covariates sex, age, hospital region, type of service, and main diagnosis at discharge as potential confounders. From all the hospitals of Portugal mainland 41 (54%) participated in the study (2093 patients). Statistical significant differences were found between patients hospitalized in AC+ versus AC- services. The hazard ratio of death for patients in AC+ services versus patients in AC- services was 0.60 (95% CI=0.37-0.97). Our study indicates that patients (<=45 years) hospitalized in a service AC+ were protected from the heat excess effect with a 40% risk reduction of death. These results support the recommendations of hospital acclimatization issued by the Portuguese Heat Wave Contingency Plan.