Assessing secondhand and thirdhand tobacco smoke exposure in Canadian infants using questionnaires, biomarkers, and machine learning

Jaclyn Parks,Kathleen E Mclean,Tim K Takaro,Allan B Becker,Malcolm R Sears,Piush J Mandhane,Russell J De Souza,Stuart E Turvey,Meghan B Azad,Padmaja Subbarao,Jeffrey R Brook,James Scott,Theo J Moraes,Lawrence Mccandless,Diana L Lefebvre

doi:10.1038/s41370-021-00350-4

Abstract

BackgroundAs smoking prevalence has decreased in Canada, particularly during pregnancy and around children, and technological improvements have lowered detection limits, the use of traditional tobacco smoke biomarkers in infant populations requires re-evaluation.ObjectiveWe evaluated concentrations of urinary nicotine biomarkers, cotinine and trans-3’-hydroxycotinine (3HC), and questionnaire responses. We used machine learning and prediction modeling to understand sources of tobacco smoke exposure for infants from the CHILD Cohort Study.MethodsMultivariable linear regression models, chosen through a combination of conceptual and data-driven strategies including random forest regression, assessed the ability of questionnaires to predict variation in urinary cotinine and 3HC concentrations of 2017 3-month-old infants.ResultsAlthough only 2% of mothers reported smoking prior to and throughout their pregnancy, cotinine and 3HC were detected in 76 and 89% of the infants’ urine (n = 2017). Questionnaire-based models explained 31 and 41% of the variance in cotinine and 3HC levels, respectively. Observed concentrations suggest 0.25 and 0.50 ng/mL as cut-points in cotinine and 3HC to characterize SHS exposure. This cut-point suggests that 23.5% of infants had moderate or regular smoke exposure.SignificanceThough most people make efforts to reduce exposure to their infants, parents do not appear to consider the pervasiveness and persistence of secondhand and thirdhand smoke. More than half of the variation in urinary cotinine and 3HC in infants could not be predicted with modeling. The pervasiveness of thirdhand smoke, the potential for dermal and oral routes of nicotine exposure, along with changes in public perceptions of smoking exposure and risk warrant further exploration.

Highlights

Tobacco smoke exposure has been studied extensively for its negative health effects and is known to be harmful to children [1]
This is similar to a Korean cohort study in which 88% of infants from non-smoking homes had infants with detectable concentrations of cotinine [33] and a study of American adolescents that found that most participants were exposed to tobacco smoke but that the majority of exposure was from light shifted to understanding secondhand (SHS) and thirdhand smoking (THS) exposure sources [32]
Our results suggest that tobacco smoke questionnaire models may not accurately explain the majority of variation in cotinine or 3HC concentrations within a population with relatively little smoking exposure

Summary

Introduction

Tobacco smoke exposure has been studied extensively for its negative health effects and is known to be harmful to children [1]. The health effects of firsthand smoking are well appreciated and research priorities have shifted to understanding secondhand (SHS) and thirdhand smoking (THS) [2,3,4]. Assessing prenatal and early life tobacco smoke exposure is important to understand and reduce childhood asthma and wheeze [7]. Questionnaires are a flexible and relatively inexpensive method of assessing exposure, but biomarkers of tobacco smoke exposure are more accurate, objective, and can be obtained with little burden to the participant using passive urine sample collection. METHODS: Multivariable linear regression models, chosen through a combination of conceptual and data-driven strategies including random forest regression, assessed the ability of questionnaires to predict variation in urinary cotinine and 3HC concentrations of 2017 3-month-old infants. The pervasiveness of thirdhand smoke, the potential for dermal and oral routes of nicotine exposure, along with changes in public perceptions of smoking exposure and risk warrant further exploration

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