Medical diagnoses of heat wave-related hospital admissions in older adults

Abstract

Heat waves have been associated with adverse human health effects, including higher rates of all-cause and cardiovascular mortality, and these health effects may be exacerbated under continued climate change. However, specific causes of hospitalizations associated with heat waves have not been characterized on a national scale. We systematically estimated the risks of cause-specific hospitalizations during heat waves in a national cohort of 23.7 million Medicare enrollees residing in 1943 U.S. counties during 1999-2010. Heat waves were defined as ≥2 consecutive days exceeding the county's 99th percentile of daily temperatures, and were matched to non-heat wave periods by county and week. We considered 50 outcomes from broad disease groups previously associated with heat wave-related hospitalizations, and estimated cause-specific relative risks (RRs) of hospital admissions on heat wave days. We identified 11 diagnoses with a higher admission risk on heat wave days, with heat stroke and sunstroke having the highest risk (RR = 22.5, [95% CI 14.9-34.2]). Other diseases with elevated risks included fluid and electrolyte disorders [(Hyperosmolality RR = 1.4, [95% CI 1.1-1.3]; Hypoosmolaltiy RR = 1.2, [95% CI 1.1-1.3])] and acute kidney failure (RR = 1.1, [95% CI 1.1-1.2]). These risks tended to be higher under more severe heat wave events. In addition, risks were higher among adults in the oldest (≥85) category (reference: 65-74) for volume depletion and heat exhaustion. Several causes of hospitalization identified are preventable, and public health interventions, including early warning systems and plans targeting risk factors for these illnesses, could reduce adverse effects of heat in the present and under climate change.

Keywords: Environmental health; Heat waves; Hospital admissions; Prevention; Public health.

Figure 1

(A–F): Relative risk estimates (95% confidence intervals) of hospital admissions on a heat wave day as compared to a matched non-heat wave day, for 50 medical diagnosis within 6 disease categories, and for the overall estimate from each category, on average across 1,943 U.S. counties during the period 1999–2010. Each diagnosis is labeled with its associated short description, with ICD-9 codes given in parenthesis. A heat wave was defined as a period of at least 2 consecutive days with temperatures exceeding the 99^th percentile of the average daily temperature for that county. A) Acute and unspecified renal failure; B) Congestive heart failure; nonhypertensive; C) Fluid and electrolyte disorders; D) Other injuries and conditions due to external causes; E) Septicemia (except in labor); F) Urinary tract infections NOS=not otherwise specified; Ac=acute; tubr=tubular; necr=necrosis; CHF=congestive heart failure; HF=heart failure; NEC=not elsewhere classified; sept=septicemia; UTI=urinary tract infection

Figure 2

(A–F): Relative risk estimates (95% confidence intervals) of hospital admissions on a heat wave day as compared to a matched non-heat wave day, across six heat wave definitions capturing increasing duration (number of days) and intensity (temperature percentile), on average across 1,943 U.S. counties during the period 1999–2010. P values from the test comparing the relative risk under the most severe (4 day, 99^th percentile) heat wave definition to the least severe (2 day, 97^th percentile) are shown in parentheses next to the name of the medical diagnosis, with asterisks (*) denoting P < 0.05. Results are shown for each of the 12 medical diagnoses having statistically significant risks under the 2 day, 99th percentile definition. A) Acute and unspecified renal failure; B) Congestive heart failure; nonhypertensive; C) Fluid and electrolyte disorders; D) Other injuries and conditions due to external causes; E) Septicemia (except in labor); F) Urinary tract infections NOS=not otherwise specified; Ac=acute; HF=heart failure; NEC=not elsewhere classified; sept=septicemia; UTI=urinary tract infection