Allergic disease in teenagers in relation to urban or rural residence at various stages of childhood

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Abstract
Background: Higher prevalences of allergic diseases and IgE antibodies to inhalant allergens have been reported for persons living in urban areas than for persons living in rural areas. Methods: Associations between cumulative incidences of allergic diseases in 1878 children aged 13–14 years and their place of residence (urban, semiurban, or rural) from birth were assessed by questionnaire (ISAAC), in order to find out whether there is a period of increased sensitivity to external influences during the first few years of life. Family history and exposure to pets, tobacco smoke, and damp were considered in multiple regression. Results: There was a significantly higher prevalence of allergic diseases with urban residence than with rural residence during the first 2 years of life (e.g., for bronchial asthma, relative risk (RR) for the first year 2.1, 95% CI 1.2–3.7). An increased risk was still found after multiple regression (RR=1.7). Semiurban residence was associated with an intermediate cumulative incidence of allergic diseases. Maternal smoking during pregnancy was associated with asthma (RR=1.4, 95% CI 1.0–2.0). Conclusions: The findings support a period of increased susceptibility during the first years of life. Whether rural lifestyle protects against allergy or whether urban pollutants contribute to allergy has to be elucidated.