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Indoor Risk Factors for Asthma in a Prospective Study of Adolescents

McConnell, Rob1; Berhane, Kiros1; Gilliland, Frank1; Islam, Talat1; Gauderman, W. James1; London, Stephanie J.2; Avol, Edward1; Rappaport, Edward B.1; Margolis, Helene G.3; Peters, John M.1

Original Articles

Background.  The risk of asthma associated with pets and other indoor exposures has been examined in both cross-sectional and prospective studies of younger children. However, there has been little investigation of the effect of the indoor environment on incident asthma in adolescents.

Methods.  Risk factors for the development of asthma were examined in a cohort of 3535 Southern California school children with no history of asthma at 1993 entry into the study, who were followed for up to 5 years. Newly diagnosed cases of asthma were identified by yearly interview report. A total of 265 children reported a new diagnosis of asthma during the follow-up period; 163 of these had reported no history of wheeze at baseline. The risk associated with indoor exposures assessed by questionnaire at entry into the study was examined using Cox proportional hazards models.

Results.  In children with no history of wheezing, an increased risk of developing asthma was associated with a humidifier (relative risk [RR] = 1.7; 95% confidence interval [CI] = 1.2–2.4), any pet (RR = 1.6; 95% CI = 1.0–2.5), or specifically a dog (RR = 1.4; 95% CI = 1.0–2.0) in the home. An estimated 32% of new asthma cases could be attributed to pets.

Conclusions.  We conclude that furry pets are a common and potentially remediable risk factor for new onset asthma in adolescents. Our results suggest that a humidifier in the home may contribute to the onset of asthma in this age group.

From 1Department of Preventive Medicine, Keck School of Medicine of the University of Southern California, Los Angeles, California;

2National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina; and

3California Air Resources Board, Sacramento, California.

Address correspondence to: Rob McConnell, Department of Preventive Medicine, 1540 Alcazar Street, Suite 236, Los Angeles, CA;

This study was supported by the California Air Resources Board (Contract A033-186), the National Institute of Environmental Health Science (Grants #1PO1ESO939581-01 and #5P30ES07048-05), the Environmental Protection Agency (Grant #R826708-01-0 and Contract #CR824034-01-3), the National Heart, Lung and Blood Institute (Grant 1RO1HL61768), and the Hastings Foundation.

Submitted 12 December 2000; final version accepted 29 November 2001.

© 2002 Lippincott Williams & Wilkins, Inc.