Assessing Helicobacter pylori infections among adults from the Navajo Nation

Dornell Pete | 2022

Advisor: Amanda Phipps

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Background: Although the burden of gastric cancer is low in the United States (US) overall, a substantial burden of gastric cancer continues to be observed in American Indians and Alaska Natives (AI/AN), particularly in the Southwest and Alaska regions of the US. In particular, gastric cancer incidence is 3.5 times higher in the Navajo Nation, a tribe of 157,000 tribal members, than in the general Arizona and New Mexico population. Contributing factors underlying this disparity are not well understood, although it is plausible that Helicobacter pylori (H. pylori), an infectious pathogen that colonizes the stomach mucosa and is a major risk factor for gastric cancer, could be a significant contributor to the elevated burden of gastric cancers in the Navajo Nation. Objectives: This dissertation presents the findings from the Navajo ABID (Assessing the microBiota and Individual Diet) study, the first study to assess risk factors for gastric cancer in two regions of the Navajo Nation. We assessed the prevalence of and risk factors for H. pylori infection and H. pylori cagA virulence gene carriage, as well as the association between diet and H. pylori infection in Navajo adults residing on the Navajo Nation. Methods:We launched a cross-sectional study in the central and northeast regions of the Navajo Nation in 2021. Demographic, health, behavioral, environmental, and diet data were collected from health and food questionnaires. H. pylori infection and cagA virulence gene status were detected from stool samples. We calculated the prevalence of H. pylori infection and odds ratios for associations between infection status and potential risk factors (including demographics, medical history of gastrointestinal conditions, family history of gastrointestinal conditions, aspirin use, body mass index, smoking, alcohol use, drinking water source, and own livestock). We used principal component analysis to identify dietary patterns and assessed the associations between dietary patterns and H. pylori infection using logistic regression. Results:We recruited and obtained data on 104 eligible adults for the Navajo ABID study. We found that 57.7% (95% CI: 47.6-67.3) of participants were infected with H. pylori and, among H. pylori-infected participants, 76.7% (95% CI: 64.0-86.6) were infected with a cagA-positive H. pylori strain. Having a history of H. pylori infection was inversely associated with H. pylori infection; no significant associations were observed with other known risk factors. We identified three dietary patterns and found that a diet pattern of Soups and Mixed dishes was positively associated with H. pylori infection in Navajo participants after adjusting for confounders; we found no significant associations between the Western or the Fruits and Vegetable pattern and H. pylori infection. No signification associations were found between selected nutrients (i.e., sodium, alcohol, vitamin C, vitamin A, vitamin E, and folate) and H. pylori infection, although positive associations with sodium and folate, and inverse associations with vitamin A, vitamin C, and alcohol were suggestive. Conclusions:The prevalence of H. pylori infection was two times higher in Navajo adults in the Navajo ABID study compared to the US population, while the prevalence of the cagA gene (77%) in H. pylori-infected participants was disproportionately higher than the US population cagA gene prevalence in whites (19%). With the exception of the observed Soups and Mixed dishes dietary pattern, few dietary factors were associated with H. pylori infection. Our findings provide a greater understanding of the burden of H. pylori and cagA-positive infections needed to inform public health prevention efforts in the Navajo Nation. These results may also allow for the design of health education material that focuses on H. pylori prevention and promotes general recommendations on healthy eating.