Background: Previous epidemiologic studies have demonstrated an inverse association between childhood exposure to oral-fecal microbes, such as Helicobacter pylori, and the development of atopic conditions, such as asthma. Recent studies have also demonstrated immune modulating effects, specifically a decrease in the cytokine profile responsible for asthma, when mice were inoculated with H. pylori virulence factors. This systematic review looks at recent cross-sectional studies to determine if H. pylori colonization is associated with decreased asthma rates.
Methods: The medical literature search utilized MEDLINE (through Ovid and PubMed), Web of Science, and Evidence Based Medicine Review and found five case-control observational studies that clearly defined asthma and H. pylori diagnosis. Studies were critically appraised and assessed with GRADE criteria.
Results: Five retrospective case-control studies were used in this systematic review. The largest of these case-control studies (7663 participants) found a significant inverse relationship between CagA positive strains of H. pylori, a specific virulence factor, and the development of asthma before age 15 (OR=0.63 (0.43-0.93)). The study was repeated with 7412 participants the following year and found a strong inverse relationship between H. pylori and presence of asthma in children (OR=0.41 (0.24-0.69)) and onset of asthma before age 5 (OR=0.58 (0.38-0.88)). The smallest of these case-control studies (526 participants) found a significant inverse relationship between CagA positive strains of H. pylori and the development of asthma (OR=.57 (CI 0.36-0.89)). The Israeli study (6959 children) found a 1.8% increased prevalence of asthma in children without H. pylori. The United Kingdom study (3244 participants) found a suggested inverse relationship between H. pylori and asthma (OR=0.78 (0.59-1.05)).
Conclusion: The findings suggest that H. pylori and other oral-fecal microbe exposure at a young age may have an immune modulating effect which either delays and/or prevents the development of asthma. Future research is needed to determine whether H. pylori virulence factors may be utilized in medicine to prevent the development of asthma without causing pathology.
Keywords: H. pylori, asthma, atopy, atopic
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