Prevalence of allergy in children in relation to prior BCG vaccination and infection with atypical mycobacteria

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Abstract
By influence on the Thl/Th2 cell balance, infectious agents may affect development of atopic allergy. In this study, we investigated whether previous BCG vaccination or infection with atypical mycobacteria might related lo the development of atopic disease. The study, which involved skin testing with mycobaeteria and answers to a questionnaire for more than 6000 children in Sweden, revealed a low prevalence of allergy among BCG‐vaccinated children who were immigrants or adopted from other countries. Vaccinated children bom in Sweden, however, did not have significantly lower allergy prevalence than age‐matched, unvaccinated children. Furthermore, the overall frequencies of skin‐test reactivity to atypical mycobacteria M. avlum and M. scrofulaceum were higher rather than lower in allergic than in nonallergic children. By contrast, there was tendency toward a lower frequency of more strongly positive skin reactions (>10mm) to mycobacteria in allergic than in nonallergic children. These findings do not support the hypothesis that early mycobacterial infections have a suppressive effect on the development of atopic disease. Earlier findings of an apparent association between atopy and lack of previous mycobacterial infection may possibly be explained by a relatively decreased ability of atopic patients to mount strong Thl cell‐mediated immune responses.