Association between homelessness and temperature-related health emergencies in the United States

Temperature-related illness (TRI) encompasses heat-related illness, such as heat exhaustion and heatstroke, and cold-related illness, such as frostbite and hypothermia. TRI is typically the result of exposure to ambient weather conditions; because of this, unhoused individuals are hypothesized to have higher risk of TRI. However, no national epidemiological studies have been completed to determine this risk. The objective of this study was to determine the association between homelessness and emergency department (ED) diagnosis of TRI in the United States. We conducted a cross-sectional study of adult ED visits in the U.S. from 2005 through 2020 using data from the National Hospital Ambulatory Medical Care Survey (NHAMCS), a nationally representative sample of non-federal ED patient visits. Housing status (housed vs. unhoused) was measured using NHAMCS patient residence category, with blank responses excluded. TRI was defined as ED clinician diagnosis of heat- or cold-related illness using ICD-9 and ICD-10 codes. Multivariable logistic regression was used to determine adjusted odds of TRI by housing status. There were 323,606 non-pediatric ED visits in the NHAMCS sample. TRI diagnosis was present in 288 (0.09%) visits. 4099 visits (0.9%) were categorized as unhoused. After adjusting for sex, mental health diagnosis, and alcohol or substance use or use disorder, the odds of TRI diagnosis in unhoused individuals was 4.08 (95% CI 2.09,7.95) compared to housed individuals. We found a higher adjusted odds of TRI diagnosis at an ED visit among unhoused individuals compared with housed individuals.