Heat-related morbidity and mortality in New England: Evidence for local policy

Background: Heat-related morbidity and mortality is a recognized public health concern. However, public health officials need to base policy decisions on local evidence, which is often lacking for smaller communities. Objectives: To evaluate the association between maximum daily heat index (HI) and morbidity and mortality in 15 New England communities (combined population: 2.7 million) in order to provide actionable evidence for local officials. Methods: We applied overdispersed Poisson nonlinear distributed lag models to evaluate the association between HI and daily (May-September) emergency department (ED) admissions and deaths in each of 15 study sites in New Hampshire, Maine, and Rhode Island, controlling for time trends, day of week, and federal holidays. Site-specific estimates were meta-analyzed to provide regional estimates. Results: Associations (sometimes non-linear) were observed between HI and each health outcome. For example, a day with a HI of 95 degrees F vs. 75 degrees F was associated with a cumulative 7.5% (95% confidence interval [CI]: 6.5%, 8.5%) and 5.1% (95% CI: 0.2%, 10.3%) higher rate of all-cause ED visits and deaths, respectively, with some evidence of regional heterogeneity. We estimate that in the study area, days with a HI >= 95 degrees F were associated with an annual average of 784 (95% CI: 658, 908) excess ED visits and 22 (95% CI: 3, 39) excess deaths. Conclusions: Our results suggest the presence of adverse health impacts associated with HI below the current local guideline criteria of HI >= 100 degrees F used to issue heat advisories. We hypothesize that lowering this threshold may lead to substantially reduced heat-related morbidity and mortality in the study area.