Socioeconomic disparities in secondhand smoke exposure among US never-smoking adults: the National Health and Nutrition Examination Survey 1988-2010.

BACKGROUND: Secondhand smoke (SHS) is a leading preventable cause of illness, disability and mortality. There is a lack of quantitative analyses on socioeconomic disparities in SHS; especially, it is not known how socioeconomic disparities have changed in the past two decades in the USA. OBJECTIVES: To examine socioeconomic disparities and long-term temporal trends in SHS exposure among US never-smoking adults aged ≥20 years. METHODS: 15 376 participants from the National Health and Nutrition Examination Survey (NHANES) 1999-2010 were included in the analysis of socioeconomic disparities; additional 8195 participants from NHANES III 1988-1994 were included in the temporal trend analysis. SHS exposure was assessed using self-reported exposure in the home and workplace as well as using serum cotinine concentrations ≥0.05 ng/mL. Individual socioeconomic status (SES) was assessed using poverty-to-income ratio. RESULTS: During the period 1999-2010, 6% and 14% of participants reported SHS exposure in the home and workplace, respectively; 40% had serum cotinine-indicated SHS exposure. Individual SES was strongly associated with SHS exposure in a dose-response fashion; participants in the lowest SES group were 2-3 times more likely to be exposed to SHS compared with those in the highest SES group. During the period 1988-2010, the prevalence declined over 60% for the three types of SHS exposure. However, for cotinine-indicated exposure, the magnitudes of the declines were smaller for lower SES groups compared with higher SES groups, leading to widening socioeconomic disparities in SHS exposure. CONCLUSIONS: SHS exposure is still widespread among US never-smoking adults, and socioeconomic disparities for cotinine-indicated exposure have substantially increased in the past two decades.