In July 2006, California experienced a heat wave of unprecedented magnitude and geographic extent–impacting the entire State. Coroners attributed 140 deaths to hyperthermia, and it has been estimated from vital statistics data that in excess of 600 heat-related deaths may have occurred over a 17-day period (July 14–30). Global warming has and will continue to increase the frequency and magnitude of extreme heat events extending their geographic breadth and placing more populations at risk. Furthermore, there is evidence that the character of heat waves in California is changing: they are progressively more often humid, consequently tending to remain hot through the night and last longer overall.
(1) To evaluate case data from coroners’ reports of hyperthermia deaths that occurred July 14 to 30, 2008, inclusive, in the context of individual risk factors and daily meteorological parameters. (2) To optimize public health intervention strategies to prevent heat-related mortality and morbidity.
Working with county and local coroners, data was compiled on 140 hyperthermia deaths to ascertain case demographics, co-morbidities, and zip code of residence, among other information. Regional indices of both maximum and minimum temperatures evaluated at 95 stations over California and Nevada were used to define, relative to local climate, the period and spatial extent of the heat wave. Locally, a heat wave was defined to occur when the 99th temperature percentile was exceeded.
Meteorologically, the 2006 heat wave over California as a whole was significant between July 14–30 with the greatest spatial extent and regional magnitude concentrated between July 21–26. Nineteen counties reported at least one death; 80% of the cases were in seven counties, most of which were in the Central Valley–a region characterized by high summertime temperatures (e.g. Sacramento, in the northern Central Valley, experiences average summertime maximum temperature of 33°C/91°F and minimum temperature of 15°C/59°F. The corresponding 99%-ile thresholds of 42.2°C/108°F and 22.8°C/73°F, were exceeded for 3 consecutive days and 7 nights, respectively, with a nighttime peak temperature of 29°C/84°F and high humidity throughout the event). Of the 140 deaths, 126 were classified as “classic heat-stroke” (CHS) and 14 as “exertional heat stroke”. 66% of cases were male. The age distribution for Hispanic cases tended to younger age groups, compared to non-Hispanic cases; this difference could not be accounted for by occupational activities. 99% of cases lived in zip codes where > 50% of residents live below the poverty guide line. The majority of CHS cases were older adults, living alone, and had at least one chronic health condition (e.g., cardiovascular (47%) or pulmonary (7%) disease; psychiatric condition (23%) or alcohol abuse/dependence (17%)). Heat exposure occurred indoors in most cases. 13% of the CHS cases were determined to have functional air conditioners that had not been used.
Discussion and Conclusion:
Case risk factors and unusual meteorological conditions during this event appear to have jointly contributed to the high death toll. Insights from this study can be translated to public health actions that diminish risk of heat-related morbidity/mortality.