The 2006 California Heat Wave: Impacts on Hospitalizations and Emergency Department Visits : Epidemiology

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Abstracts: ISEE 20th Annual Conference, Pasadena, California, October 12–16, 2008: Contributed Abstracts

The 2006 California Heat Wave: Impacts on Hospitalizations and Emergency Department Visits

Knowlton, K*; Rotkin-Ellman, M; King, G; Margolis, H G; Smith, D; Solomon, G; Trent, R§; English, P‡*

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Epidemiology 19(6):p S323, November 2008. | DOI: 10.1097/01.ede.0000340508.25106.ed
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Severe heat waves have resulted in substantial mortality in US and European cities. Global climate models project an increase in heat wave frequency, duration and severity in the future, presenting an ongoing challenge to health worldwide. While a large epidemiological literature exists on the mortality impacts of heat waves, there have been very few studies of their impacts on morbidity.


The California Department of Public Health, in conjunction with the Natural Resources Defense Council, conducted an analysis of increased hospitalizations and Emergency Department (ED) visits across the state of California during a severe heat wave in the summer of 2006. County-level hospitalizations and ED visits for all causes and for 11 cause groups were aggregated into six geographic regions. Excess morbidity and rate ratios (RRs) during the heat wave (July 15–August 1, 2006) were calculated and compared to a summer 2006 referent period by cause, age grouping, and racial/ethnic category.


During the heat wave, 16,166 excess ED visits and 1,182 excess hospitalizations occurred statewide. ED visits for heat-related causes increased across the state (RR 6.30; 95%CL = 5.67–7.01), especially in the cooler Central Coast region which includes San Francisco (RR 23.05; 95%CL = 15.05–37.10). Children (ages 0–4 years) and the elderly (ages ≥65 years) were at greatest risk. ED visits also showed significant increases for acute renal failure, cardiovascular diseases, diabetes, electrolyte imbalance and nephritis. Significantly elevated RRs for hospitalizations were observed for heat-related illnesses (RR 10.15; 95%CL = 7.79–13.43), acute renal failure, electrolyte imbalance and nephritis.


The 2006 California heat wave had a substantial effect on morbidity, including in regions with relatively modest absolute temperatures during the heat wave period. This suggests population acclimatization and adaptive capacity influenced risk. This study provides insight into those populations most vulnerable to heat, demonstrates the value of analyzing ED visits and hospitalizations, and suggests possible preventive strategies to avoid heat-related deaths in the future and in other geographic areas. This presentation will discuss the findings of the study and the implications for global health in a warming future.

© 2008 Lippincott Williams & Wilkins, Inc.