Dr. Paolo Maria Matricardi from the World Health Organization, Geneve, Switzerland, and colleagues say the findings "support the hypothesis that hygiene is a major factor contributing to the increase in...atopic sensitization in westernized countries."

Using data on 33,994 US men and women who participated in NHANES III, the researchers gathered information on sociodemographic factors, lifetime diagnosis of hay fever and asthma, skin sensitization to nine airborne allergens and peanut, and current serology for Toxoplasma gondii, herpes simplex virus 1 and 2, and hepatitis A, B and C.

Individuals who were seropositive for hepatitis A, Toxoplasma gondii, and herpes simplex virus 1 had adjusted odds ratios of 0.27 for hay fever and 0.45 for asthma compared with those who were seronegative, the researchers found.

Among subjects under 40 years of age, those who were seropositive for hepatitis A were less frequently sensitized to peanut and to all airborne allergens except cockroach than seronegative individuals, according to the report in the September issue of the Journal of Allergy and Clinical Immunology.

Dr. Matricardi's team notes that the prevalence of hay fever and asthma at or before 18 years of age was 2.7% and 0.4%, respectively, among those born before 1920; the corresponding rates among those born in the 1960s increased to 8.5% and 5.8%.

A declining exposure to food-borne and orofecal infections, Dr. Matricardi and colleagues conclude, has contributed to the increase in hay fever, asthma and atopy in developed countries.

J Allergy Clin Immunol 2002;110:381-387.