Exposure to environmental factors has been extensively studied in relation to the occurrence of respiratory diseases among children and adults. The effects of air pollution have been evaluated, and several studies indicate that respiratory symptoms may be exacerbated by living along busy roads.^1,2 Tobacco smoke is an important cause of indoor air pollution, and children exposed to passive smoking have reduced lung function, increased risk of lower respiratory tract illnesses, and acute exacerbation of asthma resulting in hospitalisation.³ Moreover, the excessive moisture found in some homes promotes mould growth and is associated with an increased frequency of irritation, allergy, and infection.^4,5

Most of the evidence on the role of chronic exposure to environmental factors in the respiratory health of schoolchildren derives from cross-sectional studies. However, there are problems in the interpretation of prevalence studies, especially when information on the exposure variables is collected in the same investigations.^6,7 We used a longitudinal approach to evaluate whether indoor and outdoor environmental exposures at baseline are associated with the risk of subsequent hospitalisation for respiratory conditions during a five year follow up of a cohort of children.

METHODS

The cohort was made up of a representative sample of children, who lived in Rome and participated in SIDRIA (Italian Studies on Respiratory Diseases and Environment) within the ISAAC phase I study,⁸ conducted from November 1994 to February 1995. Baseline data of the cohort members (6–7 years, n = 4027 from 46 elementary schools) included information on environmental risk factors, and were provided by parents through a self-administered questionnaire. Length of father’s education in years was taken as a proxy of socioeconomic status. The following environmental exposures were considered: current parental smoking at the time of the interview (maternal and paternal), presence of mould or humidity in the child’s room …