This article (2011) includes two cross-sectional studies (PARSIFAL and GABRIELA) of the prevalence of asthma and atopy with children living on Central European farms compared to a reference group. Farms were chosen as the environment that supports a wider range of microbial exposure, which is thought to give protection against the aforementioned diseases.

Both studies collected dust samples from indoors and did microbial analyses by either SSCP targeting microbial DNA, or cultury, microscopy and Gram’s staining. Over 900 samples were used for analysis. Questionnaires were used to assess respiratory and allergic symptoms and diagnoses,  farm-related exposures at various ages, and potential confounders. Children living full-time on family-run farms were classified as members of the farm group, whereas all other children were classified as members of the reference group.

The study found, that children raised on farms

• Had a wider range of microbial exposures than the children in reference groups
• Had a lower prevalence of asthma with odds ratios of 0.62 and 0.86
• Had a lower prevalence of atopy with odds ratios of 0.24 and 0.51

The wider microbial exposure explained a substantial fraction of the inverse relation between asthma, but not atopy, and growing up on a farm. This was true even when indoors.