Childhood exposure to infection and risk of adult onset wheeze and atopy

Background-The prevalence of asthma and allergic diseases in children and y oung adults is inversely associated with family size. It has been suggested that more frequent exposure to infections in a large family group, particu larly those spread by the faecal-oral route, may protect against atopic dis eases, although not all published data support this hypothesis. Whether sim ilar considerations apply to adult onset wheeze is unknown. The relationshi p between adult onset wheezing and atopy measured in adulthood and childhoo d exposure to a range of infections was investigated. Methods-A nested case control study of participants in a 30 year follow up survey was conducted. Questionnaire data on childhood infections had been o btained in a 1964 survey. In 1995 a further questionnaire on respiratory sy mptoms and other risk factors for wheezing illness was administered, total IgE, skin and RAST tests were performed, and serum was stored. In 1999 sero logical tests for hepatitis A, Helicobacter pylori, and Toxoplasma gondii w ere performed on the stored samples. Information from the 1964 questionnair es was available for 97 cases and 208 controls and serological tests were o btained for 85 cases and 190 controls. The potential risk factors were exam ined for all cases, those who reported doctor diagnosed asthma, those who d escribed persistent cough and phlegm with wheeze, and subjects stratified b y atopic status. Results-The sibship structure was similar in cases and controls. In univari ate analysis of all cases, childhood infections reported by parents as acqu ired either before or after the age of three years did not influence case:c ontrol or atopic status. Seropositivity was also similar for all cases and controls, but cases in the subgroup with chronic cough and phlegm were more likely to be seropositive for hepatitis A and H pylori. Seropositivity was unrelated to atopic status. In multivariate analyses both the effect of ha ving two or more younger siblings (OR 0.1, 95% CI 0.03 to 0.8) and of acqui ring measles up to the age of three (OR 0.2, CI 0.03 to 0.8) were significa ntly related to a lower risk of doctor diagnosed asthma. Conclusions-In these well characterised subjects, exposure to infections as measured by parental reports obtained at age 10-14 years and by serologica l tests obtained in adulthood did not influence the development of wheezing symptoms or atopic status in adulthood. However, early exposure to measles and family size may be associated with a lower risk of adult onset doctor diagnosed asthma.