title: Infections and atopy: an exploratory study for a meta-analysis of the "hygiene hypothesis".
abstract: BACKGROUND
  According to the "hygiene hypothesis" selected allergic diseases could be prevented by exposure to infectious agents during early childhood.
  
  
  METHODS
  This study was performed to assess the feasibility of a future meta-analysis on the "hygiene hypothesis" and atopic diseases. Differences concerning the potential association with a history of infectious events, in terms of magnitude and homogeneity of global risk estimates between the three major atopic diseases (i.e. atopic dermatitis, asthma and allergic rhinitis) were examined. We conducted a preliminary analysis on a sample of articles published on this topic and cited in a recent and authoritative review.
  
  
  RESULTS
  The ranges of relative risks estimates (between 0.6 and 0.8) were similar for atopic dermatitis, allergic rhinitis and asthma. Compared with asthma and allergic rhinitis, reported global risk estimates were more stable for atopic dermatitis (lowest heterogeneity). Our analysis suggests that three main categories of indirect markers of exposure to infection can be identified: 1) geographical gradient, 2) indices of potential contact with infectious agents (such as number of siblings) and 3) history of infectious events.
  
  
  CONCLUSIONS
  In this exploratory study, we chose articles cited in a single review and obtained a preliminary quantification of the association between infections and atopic diseases. The association with indirect markers of infection corresponded to 20% protection for atopic dermatitis, 30% for allergic rhinitis and 40% for asthma. In a subsequent meta-analysis, diseases should be considered separately and differences between types of exposures should be taken into account as one of the major end-points, with attention to time since exposure and disease onset.
authors.affiliation: Istituto di Ricerche Farmacologiche Mario Negri, Via Eritrea 62, I-20157 Milano, Italia.
authors.forename: G
authors.initials: G
authors.lastname: Randi
authors.forename: A
authors.initials: A
authors.lastname: Altieri
authors.forename: L
authors.initials: L
authors.lastname: Chatenoud
authors.forename: F
authors.initials: F
authors.lastname: Chiaffarino
authors.forename: C
authors.initials: C
authors.lastname: La Vecchia
mesh_terms: D001249:Asthma / Q000276:immunology*; D003876:Dermatitis, Atopic / Q000276:immunology; D004781:Environmental Exposure; D005240:Feasibility Studies; D015438:Health Behavior; D006801:Humans; D006920:Hygiene; D006967:Hypersensitivity / Q000276:immunology* / Q000517:prevention & control; D007239:Infections / Q000276:immunology*; D012221:Rhinitis, Allergic, Perennial / Q000276:immunology