Ongoing gastric acid inhibition is a confounding factor in Helicobacter pylori diagnosis.

Background: Eradication of Helicobacter pylori by antibiotics in combination with gastric acid inhibition can result in overgrowth of non-H. pylori bacterial flora. This may confound the histological detection of H. pylori at eradication control if non-specific staining methods are used.

Objective And Methods: In 18 patients treated with amoxycillin (2 weeks) and omeprazole (6 weeks), endoscopically obtained gastric juice was cultured and two biopsies of corpus, antrum and duodenum were taken before and after eradication therapy (with gastric acid inhibition still going on) for culture and for histology to assess the intragastric bacterial flora. By histology, modified Giemsa (MG) and an H. pylori-specific immunohistochemical stain (IMM) were evaluated.

Results: Median pH of gastric juice was 1.5 (n = 18) before and 7 (n = 17) after eradication therapy, when patients were still on omeprazole. After therapy, culture showed a significant decrease (P < 0.05) in mean amount of H. pylori in corpus, antral and duodenal biopsies and a significant increase of non-H. pylori flora (P < 0.05) in gastric juice, corpus, antral and duodenal mucosa. With culture as a standard, 16 and 4 biopsy specimens were scored falsely positive for H. pylori by MG and IMM, respectively, and H. pylori was not detected in 23 and 13 biopsy specimens when culture was H. pylori-positive.

Conclusion: Because of the possible presence of non-H. pylori flora after eradication therapy, the use of IMM is recommended in this situation for the histological detection of H. pylori, especially in those patients with ongoing gastric acid inhibitory therapy.