Saliva cotinine levels of mothers and infants exposed to household secondhand smoke

Abstract

INTRODUCTION: Ample evidence had shown the causal relationship between secondhand smoke (SHS) exposure and increased risks of coronary heart disease and lung cancer. SHS also affects the respiratory system of non-smoking adults and causing lower respiratory illnesses to infants. We examined the differences in the saliva nicotine levels of mothers and infants when fathers smoked at home and mothers took protective measures to prevent the infants from household SHS exposure. METHODS: Families with smoking father, non-smoking mother and infants under 18-months attended the selected Maternal and Child Health Centres (MCHCs) were invited to participate in a randomized controlled trial in evaluating the effectiveness of a family intervention in helping the fathers to quit. Fathers and mothers were invited to complete the baselines questionnaires regarding the fathers’ smoking behaviors, household smoking practices, and mothers’ actions in protecting infants from being exposed to SHS at home and their experiences in supporting fathers to quit smoking. Saliva samples were collected from infants and mothers and sent for cotinine analyses. Two dichotomous measures on household SHS exposure were reported for the presence of (1) smoking at home by fathers and (2) the adoption of any protective measures by mothers. Log transformation was applied to normalize the distribution of the cotinine levels. ANOVAs were used to compare log-cotinine levels of mothers and infants with the two household SHS exposure measures as predictors. RESULTS: 930 couples had completed the baseline questionnaires. Fathers’ mean age was 35.42 (SD_6.92) years and mothers’ mean age was 31.13 (SD_4.87) years respectively. 51.4% of infants (474/923) were boys. 74.7% of fathers (695/915) reported that they had smoked at home and 88.7% of mothers (825/899) claimed that they had taken protective measures to prevent infants from household SHS. 919 and 848 saliva samples were collected from mothers and infants respectively and successfully analysed. ANOVA results revealed that both log mothers’ and log infant’s saliva cotinine levels were significantly different in relation to the fathers’ smoking at home (mother: F = 3.96, p = .047; infant: F = 6.48, p = 0.011) but not in mother’s protective actions (mother: F = 0.16, p = 0.69; infant: F = 0.02, p = 0.88). In general, log mother’s and infant’s saliva cotinine levels were lower in the group where the father did not smoke at home. CONCLUSION: The results clearly showed that mothers and infants are vulnerable to secondhand smoke when the fathers smoked at home, and it greatly affected both the infants’ and mother’s saliva cotinine levels. Thus, helping fathers to quit is one of the best ways to reduce household SHS exposure. Although the mothers’ protective actions did not show a significant effect on the cotinine levels, maintaining smoking hygiene at home was still important as it could remind the smoking fathers not to smoke inside the home. Perhaps further studies on investigating more rigorous protective measures to prevent household SHS exposure are warranted.