Urban living as a risk factor for atopic sensitization in Swedish schoolchildren

The prevalence of atopic sensitization was compared among all pupils in three urban school classes (median age 10, 12 and 14 years, respectively) and three corresponding classes in the adjacent rural district (642 pupils in all). A written questionnaire, oral interview and skin prick testing against 7 allergens were used, with skin tests performed on 93.4 % of the urban, and 92.0 % of the rural pupils. Contact with domestic animals was much more common in the rural area. Urban living was a risk factor for at least one positive skin test to pollen or animal dander, with odds ratio (OR) 1.83 and confidence interval (CI) 1.26–2.67. This was even more pronounced for children with both positive skin test and allergic symptoms (OR 2.13; CI 1.38–3.28). An increased prevalence of positive skin prick tests in the urban area compared with the rural environment was also found for 3 individual allergens, i.e. birch pollen (OR 1.78), timothy pollen (OR 1.87) and cat dander (OR 2.29). The relative risk for positive skin test in the urban area was further increased when standardized for allergic heredity, type of dwelling, daily exposure to tobacco smoke and dampness or abnormal smell in the home. This study suggests that various adjuvant factors increase the risk of sensitization in urban environments, particularly among children with a positive family history of allergy