The impact of parental smoking on asthma and wheezing. SIDRIA Collaborative Group. Studi Italiani sui Disturbi Respiratori nell'Infanzia e l'Ambiente.

To evaluate the impact of parental smoking on childhood asthma and wheezing, we studied two random samples of subjects ages 6–7 and 13–14 years in ten areas of northern and central Italy. Standardized questionnaires were completed by parents of 18,737 children and 21,068 adolescents (response rates, 92.8% and 96.3%, respectively) about their smoking habits and the respiratory health of their children. Adolescents were asked about their respiratory health and personal smoking. We compared two groups of cases with healthy subjects: “current asthma” (children, 5.2%; adolescents, 6.2%) and “current wheezing” not labeled as asthma (children = 4.5%, adolescents = 8.5%). Exposure to smoke of at least one parent increased the relative risk of current asthma among children [odds ratio (OR) =.34; 95% confidence interval (CI) = 1.11–1.62] and of current wheezing among adolescents OR = 1.24; 95% CI = 1.07–1.44). Maternal smoking had a stronger effect than paternal smoking. Maternal smoking during pregnancy was associated with current asthma (OR = 1.62; 95% CI = 1.34–1.96) and current wheezing in children (OR = 1.31; 95% CI = 1.06–1.62); the effects were lower among adolescents. Among subjects with a negative history of parental asthma, maternal smoking was associated with current wheezing in both age groups, whereas among those with a positive history of parental asthma it was associated with current asthma in children, but not in adolescents. We estimated that 15% (95% CI = 12–19) of the current asthma cases among children and 11% (95% CI = 8.3–14) of the current wheezing cases among adolescents are attributable to parental smoking in Italy. (Epidemiology 1999;10:692–698)