Heat-related mortality during a 1999 heat wave in Chicago.

BACKGROUND During the summer of 1999, Chicago's second deadliest heat wave of the decade resulted in at least 80 deaths. The high mortality, exceeded only by a 1995 heat wave, provided the opportunity to investigate the risks associated with heat-related deaths and to examine the effectiveness of targeted heat-relieving interventions. METHODS We conducted a case-control study to determine risk factors for heat-related death. We collected demographic, health, and behavior information for 63 case patients and 77 neighborhood-and-age-matched control subjects and generated odds ratios (ORs) for each potential risk factor. RESULTS Fifty-three percent of the case patients were aged <65 years, and psychiatric illness was almost twice as common in the younger than the older age group. In the multivariate analysis, the strongest risk factors for heat-related death were living alone (OR=8.1; 95% confidence interval [CI], 1.4-48.1) and not leaving home daily (OR=5.8; 95% CI, 1.5-22.0). The strongest protective factor was a working air conditioner (OR=0.2; 95% CI, 0.1-0.7). Over half (53%) of the 80 decedents were seen or spoken to on the day of or day before their deaths. CONCLUSIONS A working air conditioner is the strongest protective factor against heat-related death. The relatively younger age of case patients in 1999 may be due to post-1995 interventions that focused on the elderly of Chicago. However, social isolation and advanced age remain important risk factors. Individual social contacts and educational messages targeted toward at-risk populations during heat waves may decrease the number of deaths in these groups.