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NEW YORK -- Children with Helicobacter pylori infection have reduced risks of asthma and allergy, researchers here reported.
NEW YORK, April 23 -- Children with Helicobacter pylori infection have reduced risks of asthma and allergy, researchers here reported.
Acquiring H. pylori during childhood led to a 21% reduction in the risk of ever having asthma at any age and a 37% reduction in childhood asthma, reported Martin J. Blaser, M.D., and Yu Chen, Ph.D., of New York University in the April 23 issue of the Archives of Internal Medicine.
However, there was no protective effect for adult-onset asthma alone, they added. Colonization with H. pylori is usually acquired before age 10.
A substantial body of work now shows an inverse relationship between H. pylori, especially cagA+ strains, and GERD. These observations, the researchers said, suggest that H pylori can protect against GERD-related asthma.
To address this hypothesis, the researchers used data from 7,663 adults in the Third National Health and Nutrition Examination Survey (NHANES III) and compared participants positive for cagA- and cagA+ strains of H pylori with those without infection.
There was no overall association between either strain of H pylori and current asthma status. However, the association for the cagA+ strain differed by age (interaction P = .02).
The presence of cagA+ strains was inversely related to ever having asthma (OR, 0.79; 95% confidence interval [CI], 0.63-0.99).
The inverse association of being positive for cagA with onset during childhood (age 15 or younger) asthma was stronger (OR, 0.63, CI, 0.43-0.93) than that for adult-onset asthma (OR, 0.97, CI, 0.72-1.32), which basically showed no protection, the researchers said.
In assessing allergic rhinitis, the researchers reported that colonization with H. pylori, especially with a cagA+ strain, was inversely associated with currently (OR, 0.77; CI, 0.62-0.96) or ever (OR, 0.77; CI, 0.62-0.94) having a diagnosis of allergic rhinitis, especially for childhood onset (OR, 0.55; CI, 0.37-0.82).
Consistent inverse associations were found between H pylori colonization and the presence of allergy symptoms in the previous year and sensitization to pollens and molds, the researchers reported.
Colonization with either cag strain was inversely associated with having one of a group of specified allergy symptoms in the previous 12 months. However, the associations were apparent only in adults younger than age 43, while those with cagA+ strains were less likely to have wheezing, stuffy, itchy or runny nose, or watery, itchy eyes in the previous year, the investigators reported (ORs ranging from 0.77 to 0.86).
Because GERD can be asymptomatic, especially in childhood, the extent of its increasing occurrence may be underestimated, the researchers wrote.
These trends and associations support the hypothesis that H. pylori, and especially cagA+ strains, could be protective against GERD, possibly due to heightened cagA+ gastric atrophy. However, the researchers said, because GERD was not evaluated in NHANES III, future studies are needed to test the GERD relationship.
The present observations, they added, are consistent with the "hygiene hypothesis" that microbial infections during childhood may prevent or diminish atopic sensitization and asthma. In particular, they said, inadequate microbial stimulation of gut-associated lymphoid tissue, a critical site for maturation of mucosal immunity, may be relevant to this mechanism.
Although the age of H pylori acquisition was not assessed in this study, the researchers wrote, in most cases it precedes the reported onsets of asthma, allergic rhinitis, and allergy. One issue, they said, is whether asthma or allergy could promote H pylori loss, for example, due to heightened antibiotic drug use.
The stronger inverse associations in younger adults provides evidence against the antibiotic hypothesis, the researchers said, since older persons should have had an increased cumulative duration of asthma or atopy and exposure to such medications compared with younger persons, the researchers said.
Treatment of H pylori was not evaluated in NHANES III, and, therefore, some participants might have had previous treatment. However, no evidence has suggested that specific treatment to eradicate H pylori differs by status of asthma and allergy.
Non-differential misclassifications of outcome and exposure would, in general, bias toward the null, indicating that the true association may be greater, the researchers wrote.
Dr. Blaser said that these findings provide evidence that the continuing disappearance of H. pylori in developed countries is related to the increase in asthma and atopic disorders.
However, how the lack of H. pylori might contribute to the pathogenesis of these disorders is not known but could relate to immunologic imbalance. Additional studies are needed to confirm these observations and to identify the mechanisms, the researchers concluded.