Accumulated evidence on Helicobacter pylori infection and the risk of asthma: A meta-analysis.

Background: Helicobacter pylori (H pylori) infection has been suggested to be related to a decreased risk of asthma, but findings in the literature are inconsistent. Objective: To quantitatively summarize the existing evidence on the association between H pylori infection and asthma risk. Methods: The PubMed database was searched for observational studies of H pylori infection in relation to the risk of asthma published in English through May 2017. Measurements of association were pooled using a meta-analytic approach and expressed as odds ratios (ORs) with 95% confidence intervals (95% CIs). Results: Twenty-four studies were identified in this meta-analysis, including 8 case-control studies composed of 1,247 cases and 2,410 controls, and 16 cross-sectional studies composed of 50,290 participants (4,185 cases and 46,105 noncases). The average H pylori infection rates were 40.01% and 48.74% in casecontrol and cross-sectional studies, respectively. Five studies subcategorized H pylori infection according to CagA status, in which 59.37% of H pylorieinfected participants were identified as having CagA positivity. Helicobacter pylori infection was significantly inversely associated with the risk of asthma in case-control studies (OR 0.83, 95% CI 0.71-0.98) but was borderline significant in cross-sectional studies (OR 0.88, 95% CI 0.76-1.02). The observed inverse association persisted for CagA-positive H pylori infection (OR 0.77, 95% CI 0.63-0.93, P for interaction =.03) but not for CagA-negative strains (OR 1.08, 95% CI 0.66-1.78). No significant difference was observed across age or region subgroups. Conclusion: The accumulated evidence supports that H pylori infection, especially CagA-positive H pylori infection, is inversely associated with the risk of asthma. (C) 2017 American College of Allergy, Asthma & Immunology. Published by Elsevier Inc. All rights reserved.