Measuring heat stress and health outcomes associated with exposure to extreme heat events: Implications for infectious disease risk

Abstract:

We have evaluated health outcomes associated with extreme heat events in Alabama, USA through retrospective analysis of birth and death records. We have also developed measures of exposure to improve estimates of heat stress in occupational and non-occupational populations through a prospective study of individual and neighborhood level temperature and markers of chronic disease management. Individual-level temperature experienced by residents (N=180) in Birmingham AL and Wilcox Cty, AL were collected for 7 days in the summer, with residents spending an extra 30 minutes daily outdoors during days 3-7 compared to baseline days (Days 1 and 2). A subset (N=46) had been previously diagnosed with Type 2 diabetes (T2D). Findings from this work suggest physiological effects pertinent to exploring the relationship between heat stress and infectious disease. Retrospective analyses suggested a 15% (95% CI: 5%, 30%) increased risk of preterm birth during extreme heat events. Increased risk of urinary tract infections and bacterial vaginosis is one hypothesis linking extreme heat events and preterm labor and delivery, although this hypothesis has not been rigorously evaluated. In our prospective analyses, a significant increase in daily steps taken was observed between baseline days and days with additional outdoor time among participants, whereas participants diagnosed with T2D had decreased morning fasting blood glucose on days with additional outdoor time, suggesting small increases in time spent outdoors in the summer may improve chronic disease management. As T2D is a prevalent pre-existing condition that increases the risk of infectious diseases, further work could examine how blood glucose levels compromise immune function, and characterize the relationship between elevation of core temperature and blood glucose levels. We have also shown that compared to weather station data alone, low cost sensors within neighborhoods may improve our evaluation of heat-health risk in both occupational and residential settings and remotely sensed data can be used to standardize estimation of exposure across urban and rural landscapes. These spatio-temporally refined measures, along with non-invasive measures of core temperature, will allow for further examination of how heat stress may affect infectious disease risk.