Health Hazards of Smoke Spring 2001
Just Released
Smoke Exposure and Hospital Admissions
The Centers for Disease Control and Prevention (CDC) conducted an investigation to determine if increases in respiratory and cardiovascular hospital admissions occurred in four Montana counties during last season's forest fires. The study was released in May 2001. Its goal was to quantify and compare the changes in hospital admission rates from 1999 (when forest fires were not a problem) to 2000 (when they were). The counties included Ravalli, with the highest exposure, Missoula, and Lewis and Clark, both with moderate exposures, and Yellowstone with low exposure. Hourly PM10 levels were used to characterize exposures. Hospital admission records were used to represent respiratory and cardiovascular admissions. The study excluded transfers, elective procedures, and admissions of nonresidents. Monthly and 3-month hospitalization rates were calculated for each year by dividing admissions by the 1999 census population for each county. Respiratory disease (chronic obstructive pulmonary disease and pneumonia) and circulatory disease (ischemic heart disease, dysrhythmia, heart failure, and cerebrovascular disease) admissions were evaluated.
Particulate levels were higher during the 12-week period in 2000 than in 1999, with mean PM10 levels of 47 µg/m3 for Ravalli County, 34.2 µg/m3 for Missoula County, and 32.6 µg/m3 for Lewis and Clark County. Hospital admission rates for the period (July, August, September) increased in 2000 for respiratory and circulatory problems, and the admissions rates were higher in the high-exposure area. However, when the data were analyzed month-by-month, a temporal exposure-response relationship between particulate levels and hospital admissions was not evident. For example, in Ravalli County the highest increases and rates of hospital admissions for respiratory and circulatory problems occurred in July—before the high smoke exposures of August. Missoula County had fewer admissions for circulatory causes in August, while Yellowstone County, the low exposure area, showed an increase. More work is needed to link hospital admissions to smoke exposure. (from R. Gwynn and J. Mott, 2001 CDC Epi-Aid #2001-07).
Note: This study relied on a single monitor to characterize exposure of an entire county. Biomarkers of smoke exposure will allow a closer link between individual exposures and hospital admissions. The study collected—but did not report—preexisting conditions and smoking data. Residential wood burning and other factors that could confound the relationship between smoke exposure and hospital admissions should be recorded. Future studies should consider alternative hypotheses, such as increased cardiovascular admissions due to anxiety over the potential loss of one's home or summer business, or exertion related to fire control activities. This study reinforces the EPA cautionary statements for individuals with respiratory and heart disease (see table 2).
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