Involuntary smoking and asthma severity in children: data from the Third National Health and Nutrition Examination Survey.

STUDY OBJECTIVES We sought to determine the indicators of asthma severity among children in the United States with high and low levels of tobacco smoke exposure. DESIGN Cross-sectional study. SETTING Nationally representative survey of participants in the Third National Health and Nutrition Examination Survey (from 1988 to 1994). PARTICIPANTS Five hundred twenty-three children with physician-diagnosed asthma. MEASUREMENTS AND RESULTS We stratified the study participants into tertiles on the basis of serum levels of cotinine (a metabolite of nicotine that indicates tobacco smoke exposure). We used logistic and linear regression modeling, adjusting for known covariates, to determine the effect of high environmental tobacco smoke exposure on the following outcomes: asthma severity (determined using reported symptom and respiratory illness frequency); lung function; physician visits; and school absence. Among our study sample, 78.6% of children had mild asthma, 6.8% of children had moderate asthma, and 14.6% of children had severe asthma. Asthmatic children with high levels of smoke exposure, compared with those with low levels of exposure, were more likely to have moderate or severe asthma (odds ratio, 2.7 95% confidence interval [CI], 1.1 to 6.8) and decreased lung function, with a mean FEV(1) decrement of 213 mL or 8.1% (95% CI, -14.7 to -3.5). CONCLUSIONS Involuntary smoke exposure is associated with increased asthma severity and worsened lung function in a nationally representative group of US children with asthma.