Background: Epidemiologic reports on the effect of microbe exposure on the development of atopy and allergic asthma are inconsistent.
Objectives: The study investigates the association between serologic markers of infections and occurrence of atopy, allergic asthma, and rhinitis among adults in Iceland, Sweden, and Estonia.
Methods: Individuals (n = 1249; mean age, 42 years) from Iceland, Sweden, and Estonia underwent a structured interview and blood sampling. Specific IgE was measured against 4 allergens, and IgG antibodies were measured against Helicobacter pylori, Toxoplasmosis gondii, hepatitis A virus, herpes simplex virus 1, Chlamydia pneumoniae, EBV, and cytomegalovirus.
Results: Nonatopic subjects more often had positive serology for Helicobacter pylori, herpes simplex virus 1, Chlamydia pneumoniae, and cytomegalovirus. Having a low number (</=3) of IgG antibodies against the various infectious agents was an independent risk factor for atopy (odds ratio [OR], 1.43; 95% CI, 1.06-1.93), allergic asthma (OR, 1.82; 95% CI, 1.12-2.98), and allergic rhinitis (OR, 1.69; 95% CI, 1.21-2.37). The proportion of atopy that can be explained by a lower number (</=3) of infections was 6.7% in Iceland, 9.2% in Estonia, and 16.4% in Sweden, and 6.7%, 48.2%, and 33.4% for allergic asthma, respectively.
Conclusion: Our data are consistent with cumulative protective effect of infections against atopy and respiratory allergies irrespective of route of infection.
Clinical implications: The study indicates what microbes or combination of microbes play a role in the complex interplay between hygiene and allergy and may contribute toward the understanding of the allergy epidemic.