BACKGROUND: Seropositivity to food-borne and orofecal microorganisms (hepatitis A virus, Helicobacter pylori, and Toxoplasma gondii ), which are considered to be markers of poor hygiene, has been reported to be associated with a lower prevalence of atopy. In contrast, colonization of the gut with Clostridium difficile, a potential intestinal bacterial pathogen, in early childhood may be associated with a higher prevalence of atopy.

OBJECTIVE: The objective of this study was to investigate the association between atopy and exposure to 2 groups of food-borne and orofecal microorganisms: (1) markers of a poor hygiene and (2) intestinal bacterial pathogens.

METHODS: A cross-sectional population-based study of 15- to 69-year-olds living in Copenhagen, Denmark, was carried out in 1990 to 1991. Atopy was defined as a positive test result for specific IgE to at least 1 of 6 inhalant allergens. Exposure to microorganisms was assessed as IgG seropositivity to microorganisms.

RESULTS: Seropositivity to 2 or 3 markers of poor hygiene (hepatitis A virus, H pylori, and T gondii ) was associated with a lower prevalence of atopy (adjusted odds ratio, 0.5; 95% CI, 0.3 to 0.8). In contrast, seropositivity to 2 or 3 intestinal bacterial pathogens (C difficile, Campylobacter jejuni, and Yersinia enterocolitica ) was associated with a higher prevalence of atopy (adjusted odds ratio, 1.7; 95% CI, 1.2 to 2.6).

CONCLUSION: Exposure to markers of poor hygiene was associated with a lower prevalence of atopy, whereas exposure to intestinal bacterial pathogens was associated with a higher prevalence of atopy. These findings raise the hypothesis that different groups of food-borne and orofecal microorganisms may have different effects on the risk of atopy.