Climate change, heat waves, and population vulnerability: Using the environmental public health tracking network for validity testing of the heat vulnerability index

Heat waves and extreme hot weather conditions have been associated with increased burdens of morbidity and mortality, but the risks are not evenly distributed throughout the population. Mapping the spatial distribution of risk for heat-related morbidity and mortality would allow public health departments to target interventions known to prevent illness and deaths during heat waves to the most vulnerable areas. Previously, a heat vulnerability index (HVI) was created that combined factors of environmental and social vulnerability, social isolation, air conditioning prevalence, and pre-existing health conditions to locate vulnerability to heat in geographic space in metropolitan areas throughout the United States. Our study attempts to verify that the intra-urban spatial distribution of vulnerability demonstrated by the HVI is valid using local health information from several public health departments that are participating in the Center for Disease Control's Environmental Public Health Tracking Network. We calculated rates of mortality and morbidity endpoints on days exceeding the 95th and 99th percentiles for apparent temperature by geographic region for 13 years (1995-2007) at the zip code level and regressed these on the HVI to see if there was a consistent relationship of increasing adverse health impacts due to heat with increasing HVI score within metropolitan areas, states, and nationally. Our results indicate that spatial mapping of vulnerability is a useful tool for local public health departments to target increasingly scarce resources for preventing adverse health outcomes due to heat waves.