High frequency of microbial overgrowth among symptomatic patients with autoimmune atrophic gastritis

BACKGROUND: Autoimmune atrophic gastritis causes achlorhydria, which may predispose to gastrointestinal microbial overgrowth (MO). We sought to evaluate the association between autoimmune atrophic gastritis and MO.METHODS: From a database of patients at our institution who had undergone MO testing (via intestinal aspirate culture or glucose or lactulose hydrogen/methane breath testing), we identified patients with autoimmune atrophic gastritis via ICD codes. We then confirmed that these patients had a histologically confirmed diagnosis. Finally we queried the electronic health record to identify patients with non-atrophic chronic gastritis who had undergone MO testing.RESULTS: We identified 52 patients with autoimmune atrophic gastritis who underwent aspirate culture; 48 (92.3%) met criteria for small intestinal bacterial overgrowth (SIBO) at a threshold of ≥103 CFU/mL, and 39 (75%) at ≥105 CFU/mL. Among patients who had multiple aspirates, 83.3% had recurrent SIBO. Among 24 patients who underwent breath testing, 11 (45.8%) tested positive, primarily reflecting intestinal methanogen overgrowth. A notable discordance was observed among seven patients who underwent both testing modalities, with five patients having a positive culture but negative breath test. Finally, comparing MO results from patients with autoimmune atrophic gastritis to those with non-atrophic chronic gastritis identified significantly higher test positivity in autoimmune atrophic gastritis (75% vs. 34.3% at ≥105 CFU/mL, P