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 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.