Background:
Cotinine is a widely-used biomarker of exposure to tobacco for both active and second-hand smoke (SHS). Given South Africa's tobacco control laws restricting smoking in public places in the last decade, we assessed the prevalence and extent of exposure to tobacco by socio-demographic characteristics, smoking status, and exposure to SHS in the home.

Methods:
Data was analysed from the South African National Health and Nutrition Examination Survey. Interview and serum cotinine biomarker data were collected. A cotinine cut-off point of 10 ng/ml for no tobacco exposure was used in the South Africa context, and values over 300 indicated heavy tobacco smoking. Weighted multiple logistic and linear regressions were used to determine the factors associated with the presence and level of cotinine.

Results:
Cotinine was detected in 63.3% of individuals aged ≥15 years (n=4621), where 28.4% had values of ≤10 ng/ml, 22% had 10-300 ng/ml, and 12.9% above 300 ng/ml. Mean cotinine was 252.6 [235.7-269.5] for current smokers and 237.9 [197.8-278.0] for smokeless tobacco users. Among current smokers, mixed race ethnicity and being male were significantly associated with higher levels of cotinine whereas mean cotinine did not vary by exposure to SHS at home. Tobacco exposure (>10 ng/ml) was found in 18.7% of never users of any tobacco product. Among never users, the odds of tobacco exposure were significantly (p< 0.05) higher for those exposed to SHS in their homes (OR=1.59), for males (1.56), African (2.16) and mixed race (2.23) ethnic groups, older ages, those residing in rural formal areas (2.57), and in low income (2.27) and intermediate income (1.66) households.

Conclusions:
The findings provide insight into the factors associated with tobacco exposure. A substantial number of never users had cotinine in their blood, which calls for increased tobacco control efforts to protect people from the harmful effects of tobacco smoke.