A case of hemorrhagic colitis after influenza A infection.

The pandemic (H1N1) influenza virus continues to be the predominant circulating virus in both the northern and southern hemispheres. In February 2009, during the early stage of the worldwide H1N1 influenza virus (influenza A) pandemic, we experienced a case of hemorrhagic colitis after infection with influenza A. A 21-year-old man with no serious disease in his past history visited our hospital with chief complaints of a high body temperature and pharyngeal pain. A diagnosis of influenza A was made using a rapid diagnosis kit (Capilia Flu A+B), and the patient was admitted to our hospital. After admission, the patient complained of a lower abdominal pain, diarrhea, and hematochezia. An emergency colonoscopy revealed active bleeding colitis from the sigmoid to descending colon. Hemorrhagic colitis was confirmed by the pathological findings of a punch biopsy specimen. After the administration of an antiviral drug, zanamivir hydrate (10 mg/d), the patient's general condition and colonoscopic findings improved significantly. The findings of both sequential colonoscopies and intestinal histology strongly suggested that infection with influenza A could induce hemorrhagic colitis, though the incidence is quite low.