High levels of cotinine in non-smokers indicate passive exposure to tobacco smoke. This study aims to evaluate variations in salivary cotinine cut-offs to discriminate smokers and non-smokers before and after the implementation of smoke-free legislation (Law 28/2005 and Law 42/2010) in a sample of the adult population of Barcelona, Spain.
This longitudinal study analyzes salivary cotinine samples and self-reported information from a representative sample (n = 676) of the adult population from Barcelona before and after the approval of smoke-free legislation. We calculated the receiver operating characteristic (ROC) curves, to obtain optimal cotinine cut-off points to discriminate between smokers and non-smokers overall, by sex and age, and their corresponding sensitivity, specificity, and area under the curve. We used linear mixed-effects models, with individuals as random effects, to model the percentage change of cotinine concentration before and after the implementation of both laws.
The mean salivary cotinine concentration was significantly lower post-2010 law (−85.8%, p < 0.001). The ROC curves determined that the optimal cotinine cut-off points for discriminating non-smokers and smokers were 10.8 ng/mL (pre-2005 law) and 5.6 ng/mL (post-2010 law), with a post-2010 law sensitivity of 92.6%, specificity of 98.4%, and an area under the curve of 97.0%. The post-2010 law cotinine cut-off points were 5.6 ng/mL for males and 1.9 ng/mL for females.
The implementation of Spanish smoke-free legislation was effective in reducing secondhand smoke exposure and, therefore, also in reducing the cut-off point for salivary cotinine concentration. This value should be used to better assess tobacco smoke exposure in this population.
- • Cotinine cut-offs have changed after implementing smoke-free legislation in Spain.
- • The cut-off point to discriminate smokers from nonsmokers decreased by near 86%.
- • Spanish smoke-free legislation was effective reducing secondhand smoke exposure.
Smoking is considered a major risk factor for the health of both smokers and people exposed to smoke . According to the World Health Organization (WHO), eight million people died from tobacco use in 2020 and around one million of those deaths were of non-smokers exposed to second-hand smoke (SHS) . It is estimated that around 15% of the global population were smokers in 2018 . To attenuate the tobacco epidemic, the WHO Framework Convention on Tobacco Control (WHO FCTC) reaffirmed the necessity of a consistent tobacco control legislation aiming at reducing demand, in addition to tax increase and regulation of tobacco producers and sellers, which several parties have already adopted . In Spain, two laws came into effect. The first one (Law 28/2005) came into effect on the 1st of January 2006 and supposed a great improvement in public health since this law decreased the prevalence of smokers in the young population, as well as the acute myocardial infarction morbidity and the prevalence of SHS exposure in non-smokers , but it still allowed smoking in some hospitality sectors. Hence, this law did not fully protect the population against passive smoking . The second one (Law 42/2010) came into effect on the 2nd of January 2011, extending the prohibition of smoking in all public indoor areas without exceptions and in some outdoor areas . With both laws in place, secondhand smoke exposure has since been significantly reduced .