Extreme temperatures and mortality: assessing effect modification by personal characteristics and specific cause of death in a multi-city case-only analysis

Abstract

Background: Extremes of temperature are associated with short-term increases in daily mortality.

Objectives: We set out to identify subpopulations and mortality causes with increased susceptibility to temperature extremes.

Methods: We conducted a case-only analysis using daily mortality and hourly weather data from 50 U.S. cities for the period 1989-2000, covering a total of 7,789,655 deaths. We used distributions of daily minimum and maximum temperature in each city to define extremely hot days (>/= 99 th percentile) and extremely cold days (</= 1st percentile) , respectively. For each (hypothesized) effect modifier, a city-specific logistic regression model was fitted and an overall estimate calculated in a subsequent meta-analysis.

Results: Older subjects [odds ratio (OR) = 1.020 ; 95% confidence interval (CI) , 1.005-1.034], diabetics (OR = 1.035 ; 95% CI, 1.010-1.062) , blacks (OR = 1.037 ; 95% CI, 1.016-1.059) , and those dying outside a hospital (OR = 1.066 ; 95% CI, 1.036-1.098) were more susceptible to extreme heat, with some differences observed between those dying from a cardiovascular disease and other decedents. Cardiovascular deaths (OR = 1.053 ; 95% CI, 1.036-1.070) , and especially cardiac arrest deaths (OR = 1.137 ; 95% CI, 1.051-1.230) , showed a greater relative increase on extremely cold days, whereas the increase in heat-related mortality was marginally higher for those with coexisting atrial fibrillation (OR = 1.059 ; 95% CI, 0.996-1.125) .

Conclusions: In this study we identified several subpopulations and mortality causes particularly susceptible to temperature extremes. This knowledge may contribute to establishing health programs that would better protect the vulnerable.

Figure 1

Cutoff points used to define extremely cold days (1st percentile of daily maximum temperature) and extremely hot days (99th percentile of daily minimum temperature) in each of the 50 U.S. cities during the period 1989–2000.

Figure 2

Modification by subject characteristics of the effect of extreme hot temperature on cardiovascular mortality and noncardiovascular mortality: results from the meta-analysis of 42 U.S. cities during the period 1989–2000. Estimates represent the relative odds of dying on an extreme temperature day for persons who had the condition (e.g., being female) compared with persons who did not have the condition.