Risk factors influencing hospitalizations due to heat-related illnesses: Patterns of hospitalization use during heat events

Background: Global warming has increased the frequency and intensity of extreme heat events, behooving researchers and public health officials to understand the causes and outcomes of heat-related illnesses (HRIs), usually termed heat stroke, heat exhaustion and heat stress. Many studies have focused on heat related mortality, though there is a dearth in knowledge regarding such heat-related morbidity. This research identifies and describes populations that are hospitalized due to HRI. Prior studies have shown that populations in geographic regions that are not acclimated to heat and urban areas may suffer disproportionally higher rates of HRI. Additionally geospatial factors are analyzed to determine if they influence hospitalizations due to heat-related illness. Methods: The study design is a pooled cross-sectional analysis of secondary data, the Nationwide Inpatient Sample (NIS), from 2001 to 2010. Descriptive statistics were conducted to identify populations hospitalized due to HRIs. Hierarchical modeling was also employed to identify relationships between individual, hospitals and geographical factors that impact hospitalizations. This study is among the first to use a large data set and expansive time period to analyze heat-related morbidity and incorporate multi-level modeling with geographical factors to determine environmental risk factors for HRI hospitalizations. Results: Preliminary results indicate that hospitalizations due to heat-related illness increased over the study period, 2001 to 2010. Descriptive statistics show higher hospitalizations in infants, elderly, men and lower socioeconomic populations. Multilevel modeling shows urban areas and areas in the northeast and mid-west influencing rates of hospitalizations for HRIs. Conclusion: The focus of most research has been on heat-related mortality. This analysis seeks to broaden our understanding of health-related morbidity and the individual and environmental risk factors that influence hospitalizations. These findings offer the potential to direct policy for more strategic interventions as well as improve data collection and analyses for heat-related hospitalizations.