Association of tobacco smoke exposure and respiratory syncitial virus infection with airways reactivity in early childhood

Exposure to infectious agents and environmental tobacco smoke are thought t o induce bronchial hyperresponsiveness (BHR). This study was undertaken to determine the effects of passive exposure to tobacco smoke and respiratory syncitial virus (RSV) lower respiratory infection (LRI) during infancy on t he occurrence of BHR in the first 2 years of life. Eighty-six cases of docu mented RSV (mean age, 188 days) and 78 controls (mean age, 162 days) were e nrolled from the clinic and in-patient service of a single hospital. None h ad a history of prior LRI. Subjects were studied at 6-month intervals up to 19 months of age with a standardized respiratory illness and parental smok ing questionnaire, partial expiratory flow-volume curves by the "hug" (rapi d thoracic compression) technique, and methacholine challenge. Exposure to maternal and paternal cigarette smoking, maternal history of as thma, and mold exposure were associated with decreased levels of length-cor rected maximal flow at functional residual capacity (V'(maxFRC)). RSV-LRI w as not related to V'(maxFRC). After adjustment Of V-maxFRC for these factor s. V'(maxFRC) was a significantly and positively correlated with a methacho line concentration provoking a 40% fall in V'(maxFRC) (PC40) and negatively correlated with dose-response slope. After adjustment for V'(maxFRC), ther e were no independent effects of tobacco smoke exposure or RSV-LRI on metha choline responses. These data do not support a role for RSV as a risk factor for airways react ivity in childhood and indicate that exposure to tobacco smoke affects airw ays reactivity through its effects on airways. (C) 2001 Wiley-bss. Inc.