Impact of Heat Events on Emergency Department Visits

BACKGROUND: Due to climate change, it is expected that the number of extreme heat events will increase in the future. Many studies have examined mortality associated with heat, but not many have examined morbidity and specific causes associated with emergency department visits over multiple years.

OBJECTIVE: We identified specific causes associated with heat related emergency department visits during heat events and estimated their cause specific risk using historical data.

METHODS: We aggregated daily counts of emergency visits from hospitals in Northern Illinois participating in the Cook County syndromic surveillance system, ESSENCE, for specific syndromes including cardiovascular disease, acute myocardial infarction, stroke, diabetes, acute renal disease, nephritis, electrolyte disorder, and heat stress/stroke related visits from 2009 through 2014. A matched analysis of time-series data of daily aggregate counts of emergency department visits was performed using Poisson regression comparing heat event periods to non-heat event periods to calculate the relative risk. Heat events were defined as 2 or more consecutive days with daily maximum temperatures above the 97^th, 98^th, and 99^th percentiles of the average daily temperature. Non-heat reference periods were matched to the heat event periods by including the same number of days and same days of week, as long as it did not occur within three days of a heat event period.

RESULTS: Risks for heat stress/stroke, acute renal disease, electrolyte disorder, and nephritis were significantly higher for all heat event periods relative to matched non-heat event periods. Relative risks for these syndromes, for the 99^thpercentile temperature heat events were 42.41 (95% CI 23.57 – 76.29) for heat stress/stroke, 1.87 (95% CI 1.40 – 2.48) for acute renal disease, 1.81 (95% CI 1.62 – 2.01) for electrolyte disorder, and 1.26 (95% CI 1.06 – 1.51) for nephritis. Risks for cardiovascular disease, acute myocardial infarction, stroke, and diabetes were not significantly increased for any of the heat event periods.

CONCLUSIONS: Periods of heat events were associated with increased risks of emergency department visits for heat stress/stroke, acute renal disease, electrolyte disorder, and nephritis. In addition to monitoring heat stress/stroke emergency visits during heat waves, acute renal disease, electrolyte disorder, and nephritis are additional syndromes that should be monitored to determine the effect heat events have on the community.