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BACKGROUND: To reduce the public’s exposure to secondhand smoke, the Michigan legislature passed the Dr. Ron Davis Smoke Free Air (SFA) law. Effective May 1, 2010, the SFA law banned smoking in all public areas, including workplaces, restaurants and bars. Secondhand smoke is a known asthma trigger. According to the 2012 Michigan Behavioral Risk Factor Survey, 1 in 10 adults in Michigan have asthma and asthma disproportionately affects blacks and women. This study examines whether enactment of the SFA law associates with reduced asthma hospitalizations in Michigan adults and if the SFA law differentially affects adult asthma hospitalizations by race and sex.
METHODS: Our study used the Michigan Inpatient Hospital Database (MIDB). The MIDB is assembled by the Michigan Health and Hospital Association (MHA) and comprises the discharge abstracts from almost all acute care hospitals in Michigan. Adult asthma hospitalizations were defined as 25-64 year olds with a primary ICD9 diagnosis code of 493.xx who were discharged between January 1, 2002 and June 30, 2012. We used Poisson regression to model the rate of asthma hospitalizations before and after the ban, adjusting for sex, race, age, insurance type and month of year. We also stratified the data by race and sex to identify potential differences in post-law asthma hospitalizations between these groups.
RESULTS: With adjustments for race, sex, age, insurance type and month of year, there was a 10% decrease in adult asthma hospitalizations (P<0.0001, 95% confidence interval [CI], 9% to 13%) comparing the immediate month prelaw to postlaw, resulting in an estimated 750 fewer adult asthma hospitalizations annually. Analysis by race showed a significant difference in the asthma hospitalization rates: blacks had an 8% decrease in hospitalizations (P<0.0001, CI, 6% to 11%) comparing the immediate month prelaw to postlaw, while whites had a 16% decrease in hospitalizations (P<0.0001, CI, 13% to 18%). There was no significant difference in pre to post law asthma hospitalizations by sex.
CONCLUSIONS: This study is the first to demonstrate a population-wide reduction in adult asthma hospitalizations following the SFA law. Racial analysis showed that whites benefited more from enactment of the SFA law than blacks. While these results support continued implementation of the SFA law, more work is needed to determine the causes for these disparate health benefits.