CHILDHOOD ASTHMA AND INDOOR ENVIRONMENTAL RISK-FACTORS

In a case-control study carried out in Montreal, Quebec, Canada, betwe en 1988 and 1990, indoor environmental factors were studied in relatio n to the incidence of asthma among 3- and 4-year-old children. Cases ( n = 457), whose parents were recruited at a hospital emergency room, w ere children who had a first-time diagnosis of asthma (International C lassification of Diseases, Ninth Revision, code 493) made by a pediatr ician. Controls (n = 457) were chosen from family allowance files and were matched with case children on age and census tract. A telephone i nterview was administered to the children's parents. A 20% feasibility subsample was chosen to wear a nitrogen dioxide monitoring badge duri ng a 24-hour period. Multiple conditional logistic regression analysis showed that after personal susceptibility factors were controlled for , the following were independent risk factors for asthma: the mother's heavy smoking (odds ratio (OR) = 2.77, 95% confidence interval (Cl) 1 .35-5.66), use of a humidifier in the child's room (OR = 1.89. 95% Cl 1.30-2.74), and the presence of an electric heating system in the home (OR = 2.27, 95% Cl 1.42-3.65). The presence of other smokers in the h ome was not quite significant (OR = 1.82, 95% Cl 0.98-3.38). A history of pneumonia, the absence of breast feeding, and a family history of asthma were also significant risk factors. In a separate unmatched mul tivariate analysis of subjects who had worn the nitrogen dioxide badge , there was a dose-response relation between nitrogen dioxide (in part s per billion) and asthma. These results confirm the role of susceptib ility factors in asthma and show that indoor environmental factors con tribute to the incidence of asthma.