URINARY COTININE AND PARENT HISTORY (QUESTIONNAIRE) AS INDICATORS OF PASSIVE SMOKING AND PREDICTORS OF LOWER RESPIRATORY ILLNESS IN INFANTS

Studies of the effects of passive smoking on lower respiratory illness (LRI) have relied on questionnaires to measure exposure. We studied t he association between two measures of passive smoking and the inciden ce of acute LRI in infants. We analyzed data from a community-based co hort study of respiratory illness during the first year of life in Nor th Carolina. The incidence of LRI was determined by telephone calls at 2-week intervals. Environmental, demographic, and psychosocial risk f actors for LRI were measured during home interviews. Tobacco smoke exp osure was measured as the mean number of cigarettes smoked per day in the infant's presence. Smoke absorption by the infants was measured by the urinary cotinine/ creatinine ratio. Of the 485 infants in the stu dy, 325 (67%) had telephone follow-up and at least two home interviews . In bivariate analyses, reported tobacco smoke exposure and urinary c otinine were associated with LRI. Only the association between reporte d exposure and LRI remained significant after adjusting for confounder s, [adjusted incidence of LRI (episodes/child-year) nonexposed: 0.6; l ess than or equal to 10 cigarettes/day: 0.9 (RR 1.5, 95% CI: 1.1, 2.0) ; >10 cigarettes/day: 1.3 (RR 2.2, 95% CI: 1.3, 3.8)]. We conclude tha t infants reportedly exposed to tobacco smoke have an increased incide nce of LRI. There are differences between questionnaire and biochemica l measures of passive smoking. Urinary cotinine will not necessarily i mprove the validity of studies of the relationship of passive smoking to LRI in infants. (C) 1997 Wiley-Liss, Inc.