Trends in Secondhand Smoke Exposure, 2011−2018: Impact and Implications of Expanding Serum Cotinine Range

Introduction: The impact of defining secondhand smoke exposure among nonsmokers using an expanded serum cotinine range is currently unknown.Methods: This study assessed the trends in secondhand smoke exposure prevalence among a nationally representative sample of 23,753 U.S. nonsmokers aged >3 years. Serum cotinine ranges of 0.05-10 ng/mL (established) and of 0.015-10 ng/mL (expanded) were analyzed in 2021 using data from the 2011-2018 National Health and Nutrition Examination Survey.Results: During 2011-2018, the percentage of people with a serum cotinine range of 0.05-10 ng/mL remained stable (25.3% to 24.6%) across most sociodemographic subgroups but declined significantly among adult Mexican Americans aged >20 years (23.9% to 14.1%). However, the percentage of people with serum cotinine range of 0.015-10 ng/mL significantly declined (58.3% to 52.3%) among male individuals (60.9% to 55.0%), among female individuals (56.2% to 50.0%), among adults aged >20 years (55.8% to 49.2%), among Mexican Americans (60.9% to 41.2%), among people with a college degree or higher (44.4% to 36.0%), among those who rented their housing (71.7% to 62.5%), among people not living with someone who smoked inside the home (56.1% to 50.0%), and among Mexican Americans aged >20 years (60.9% to 39.1%) (all p<0.05 for linear trend test).Conclusions: Expanding the serum cotinine range to 0.015-10 ng/mL more than doubles the estimated proportion of U.S. nonsmokers exposed to secondhand smoke. In contrast to a serum cotinine range of 0.05-10 ng/mL, it suggests that progress has been made in reducing population-level secondhand smoke exposure during 2011-2018, especially among nonsmokers experiencing lower exposure levels. Published by Elsevier Inc. on behalf of American Journal of Preventive Medicine.