Decreasing trend in passive tobacco smoke exposure and association with asthma in U.S. children.

In this study, we assessed trends of serum cotinine levels over time among US children ages 3-11 years and compared the risk of asthma in groups exposed to passive tobacco smoke. We utilized National Health and Nutrition Examination Survey (NHANES) data collected from 2003 to 2014 (n = 8064). Serum cotinine level, household smoker status, asthma status, and sociodemographic information were extracted for multiple regression analyses. The adjusted biannual change in log (cotinine) in comparison to earlier NHANES survey cycles was - 0.196 (p < 0.001) overall, - 0.055 (p = 0.089) among children with household smoker(s), and - 0.129 (p < 0.001) among children without. The proportion of children living with household smokers decreased from 24.9% in the 2003-2004 cycle to 11.4% in the 2013-2014 cycle. The adjusted odds ratios (ORs) for asthma were 1.34 (95% confidence interval (CI): 1.00-1.80; 2nd tertile vs 1st tertile) and 1.69 (95%CI: 1.25-2.29; 3rd tertile vs1st tertile), respectively. Highly exposed asthmatic children, in the 3rd cotinine tertile (>0.13 ng/mL), were primarily Non-Hispanic Black (61.0%) and whose family incomes were below poverty guidelines. Overall results reveal passive smoke exposure level among children ages 3-11 in the US decreased over the study period. Nevertheless, higher exposure to passive smoke is still associated with higher odds of childhood asthma. Targeted smoking cessation interventions in clinical practices are needed to reduce tobacco smoke exposure and related asthma risk in children, particularly in low-income and minority groups.