Detection of type B influenza virus genes from biopsied gastric mucosa

We previously reported the existence of type B influenza genes in the gastric mucosa of three patients. The purpose of the present study was to further characterize gastric mucosal infection with type B influenza virus, in which the natural host is limited to humans. Reverse transcription polymerase chain reaction (PCR) and nucleotide sequential analyses were performed to detect type B influenza virus genes in gastric mucosa that was biopsied in the summer, when influenza was not epidemic. Statistical analyses of the clinical backgrounds of the patients were also performed. The nucleoprotein genes of type B influenza virus were detected and confirmed in 37 of 80 patients by sequence analyses of the second PCR products, although they were not detected in the first PCR products. The three patients who were receiving acid suppression therapy who were positive for the influenza virus nucleoprotein gene 37 months previously were found to be positive again. Nucleotide sequential analyses of the nucleoprotein gene revealed two missense mutations from the reference strain, suggesting the characteristics of persistent influenza virus infection. Statistical analyses of the patients' clinical backgrounds showed a correlation between influenza RNA positivity in gastric mucosa and acid inhibition therapy. These results suggest that influenza viruses infect and probably persist in the gastric mucosa under conditions of acid suppression.