BACKGROUNDThe prevalence of asthma and allergic diseases in children and young adults is inversely associated with family size. It has been suggested that more frequent exposure to infections in a large family group, particularly those spread by the faecal-oral route, may protect against atopic diseases, although not all published data support this hypothesis. Whether similar considerations apply to adult onset wheeze is unknown. The relationship between adult onset wheezing and atopy measured in adulthood and childhood exposure to a range of infections was investigated.
METHODSA nested case control study of participants in a 30 year follow up survey was conducted. Questionnaire data on childhood infections had been obtained in a 1964 survey. In 1995 a further questionnaire on respiratory symptoms and other risk factors for wheezing illness was administered, total IgE, skin and RAST tests were performed, and serum was stored. In 1999 serological tests for hepatitis A, Helicobacter pylori, and Toxoplasma gondii were performed on the stored samples. Information from the 1964 questionnaires was available for 97 cases and 208 controls and serological tests were obtained for 85 cases and 190 controls. The potential risk factors were examined for all cases, those who reported doctor diagnosed asthma, those who described persistent cough and phlegm with wheeze, and subjects stratified by atopic status.
RESULTSThe sibship structure was similar in cases and controls. In univariate analysis of all cases, childhood infections reported by parents as acquired either before or after the age of three years did not influence case:control 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 having two or more younger siblings (OR 0.1, 95% CI 0.03 to 0.8) and of acquiring measles up to the age of three (OR 0.2, CI 0.03 to 0.8) were significantly related to a lower risk of doctor diagnosed asthma.
CONCLUSIONSIn these well characterised subjects, exposure to infections as measured by parental reports obtained at age 10-14 years and by serological 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.


Keywords: childhood infections; family size; adult onset wheeze; asthma; atopy