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.