Novel Influenza (H1N1) Infection Could Cause Gastrointestinal Illness, but Not Significantly - Result of Epidemiological Survey and Antiviral Treatment Influences

[Background] There was pandemic infection of the novel influenza (H1N1) all over the world in the last winter (2009-2010 ). We have cared the novel influenza patients including adults and children in the department of General and Intensive Care Medicine. We present this study referring to gastrointestinal illness in H1NI during the last winter, because there have been very few reports about it associated with the novel influenza. [Method] Persons with fever and/or some influenza-like symptoms during 6 months from July to March 2010, were studied. Novel influenza was diagnosed by detection of viral antigen using immunochromatography assay (IC). We used two commercialized rapid IC kits (QuicNaviFluTM, OTSUKA PHARMACEUTICAL Co., LTD, Tokyo, Japan and Capilia FLU A+BTM, TAUNS LABORATORIES INC. Numazu, Japan ) for the diagnosis of novel influenza (H1N1). These kits are recommended as an authoritative rapid test for H1NI and widely indicated in Japan. We decided it H1NI when the rapid IC assay indicated type A infection. To understand gastrointestinal symptoms (diarrhea, vomiting, and abdominal pain ), all patients were classified into 4 groups; A group is composed of persons with positive influenza A check (medicated with an antiviral agent ), B group with negative influenza A check, C group without influenza check and medicated with oseltamivir, and D group without influenza and medicated with zanamivir. [Result] H1NI was diagnosed in 1567 out of 6859 suspicious patients by rapid IC assay. Gastrointestinal symptom were observed; 41 diarrhea (2.6%), 94 vomiting(6.0%), 37 abdominal pain (2.4%) respectively. Antiviral medication for treatment of H1NI infection was indicated to 3132 patients (1954 children and 1178 adults). There was no significant difference between Group A and Group B about gastrointestinal symptoms both in children and adults. No difference was found between group C and Group D about gastrointestinal symptom. There was no death due to H1NI through out the period in our department. [Conclusion] Nausea and vomiting were most frequently observed in children and adolescences with H1NI, followed by abdominal pain and diarrhea. They were not significant and further examination and treatment were not essential. Antiviral treatment ( oseltamivir and zanamivir ) could cause vomiting in only 0.5%, less than reported previously.