Impact of Heat on Respiratory Hospitalizations among Older Adults in 120 Large US Urban Areas.

Abstract

Extreme heat exposure is a well-known cause of mortality among older adults. However, the impacts of exposure on respiratory morbidity across US cities and population subgroups is not well understood. A nationwide study to determine the impact of high heat on respiratory disease hospitalizations among older adults (65+) living in the 120 largest US cities between 2000-2017. Daily rates of inpatient respiratory hospitalizations were examined with respect to variations in ZIP-code-level daily mean temperature and heat index. For each city, we estimated cumulative associations (lag-days 0-6) between warm-season heat (June-September) and cause-specific respiratory hospitalizations using time-stratified conditional quasi-Poisson regression with distributed lag non-linear models. We estimated nationwide associations using multivariate meta-regression and updated city-specific associations via best linear unbiased prediction. With stratified models, we explored effect modification by age, sex, and race (Black/white). Results were reported as percent change in hospitalizations at high temperatures (95th percentile) compared to median temperatures for each outcome, demographic group, and metropolitan area. We identified 3,275,033 respiratory hospitalizations among Medicare beneficiaries across 120 large US cites between 2000 and 2017. Nationwide, 7-day cumulative associations at high temperatures, resulted in a 1.2% (0.4%, 2.0%) increase in hospitalizations for primary diagnoses of all-cause respiratory disease, primarily driven by increases in respiratory tract infections [1.8% (0.6%, 3.0%)], and chronic respiratory diseases/respiratory failure [1.2% (0.0%, 2.4%)]. Stronger associations were observed when exposure was defined using the heat index instead of temperature. Across the 120 cities, we observed considerable geographic variation in the relative risk of heat-related respiratory hospitalizations, and we observed disproportionate burdens of heat-related respiratory hospitalizations among the oldest beneficiaries (85+ years), and among Black beneficiaries living in South Atlantic cities. During the 18-year study period, there were an estimated 11,710 excess respiratory hospitalizations due to heat exposure. Results suggest that high temperature and humidity contribute to exacerbation of respiratory tract infections and chronic lung diseases among older adults. Geographic variation in heat-related hospitalization rates suggests that contextual factors largely account for disproportionate burdens, and area-level influences should be further investigated in multi-city studies.