CROSS-SECTIONAL RETROSPECTIVE STUDY OF PREVALENCE OF ATOPY AMONG ITALIAN MILITARY STUDENTS WITH ANTIBODIES AGAINST HEPATITIS-A VIRUS

Objective: To investigate the working hypothesis that common infection s occurring early in life prevent atopy. Design: Cross sectional, retr ospective study of young Italian men with results for hepatitis A sero logy and atopy. Setting: Air force school for military students in Cas erta Italy. Subjects: 1659 male students aged 17-24, most of whom (90% ) were from central and southern Italy. Main outcome measures: Skin se nsitisation and specific IgE antibodies to locally relevant airborne a llergens; diagnosis of respiratory allergy (asthma or rhinitis, or bot h); hepatitis A seropositivity. Results: 443 of the 1659 subjects (26. 7%) were positive for hepatitis A virus antibody. Atopy was less commo n among seropositive than seronegative subjects according to skin sens itization (weal reaction greater than or equal to 3 mm) to one or more allergens (21.9% (97/443) v 30.2% (367/1216), P<0.001); polysensitisa tion (sensitive to three or more allergens) (2.7% (12/443) v 6.4% (78/ 1216), P<0.01); high specific IgE concentration (9.7% (43/443) v 18.4% (224/1216), P<0.00005); and lifetime prevalence of allergic rhinitis or asthma, or both (8.4% (37/443) v 16.7% (203/1216), P<0.001). Hepati tis A seropositivity remained inversely associated with atopy after ad justing for father's education, the number of older siblings, and the area of residence (based on the number of inhabitants). The prevalence of atopy was constantly low among seropositive subjects, whatever the number of older siblings; by contrast, it increased with a decreasing number of older siblings among seronegative subjects. Conclusion: Ind irect but important evidence is added to the working hypothesis as com mon infections acquired early in life because of the presence of many older siblings (among seronegative subjects) or because of unhygienic living conditions (among seropositive subjects) may have reduced the r isk of developing atopy.