THE ROLE OF PASSIVE SMOKING IN THE DEVELOPMENT OF BRONCHIAL OBSTRUCTION DURING THE FIRST 2 YEARS OF LIFE

We assessed the effect of exposure to environmental tobacco smoke on t he risk of developing bronchial obstruction in a 2-year cohort study o f 3,754 children born in Oslo, Norway, during a period of 15 months in 1992-1993. We collected questionnaire information on the child's heal th and environmental exposures at birth and when the child was age 6 m onths (follow up rate = 95%), 12 months (92%), 18 months (92%), and 24 months (81%). The outcome of interest was defined as two or more epis odes of bronchial obstruction or one obstruction lasting more than 1 m onth, and it was verified by a specialist group evaluating data from q uestionnaires, clinical examinations, and health records. The risk of bronchial ob struction was increased in children exposed to environmen tal tobacco smoke (cumulative incidence = 0.109) compared with unexpos ed children (0.071), with an adjusted odds ratio of 1.6 [95% confidenc e interval (CI) = 1.3-2.1]. The effect was seen for maternal smoking a lone (odds ratio = 1.6; 95% CI = 1.0-2.6), paternal smoking alone (odd s ratio = 1.5; 95% CI = 1.1-2.2), and both parents smoking (odds ratio = 1.5; 95% CI = 1.0-2.2). There was no clear exposure-response patter n. The findings indicate that exposure to environmental tobacco smoke such as is experienced in Norwegian housing increases the risk of deve loping bronchial obstruction during the first 2 years of life.