Frequent Detection of Pandemic (H1N1) 2009 Virus in Stools of Hospitalized Patients

Abstract

A novel subtype of influenza A virus called pandemic (H1N1) 2009 virus showed global outbreaks in 2009. Previous studies reported that gastrointestinal symptoms such as diarrhea, vomiting, and abdominal pain were frequent in patients with pandemic (H1N1) 2009 virus infection (3, 4, 5). However, the frequency of viral shedding in this pandemic (H1N1) 2009 virus infection was not well known. We recovered pandemic (H1N1) 2009 virus from stools of hospitalized H1N1-positive patients. From 10 November to 31 December 2009, 1,774 patients were diagnosed as having pandemic (H1N1) 2009 virus infections by real-time reverse transcription-PCR (RT-PCR) from nasopharyngeal swab samples in a tertiary-care hospital located in Seoul, South Korea. Among them, 96 patients required hospitalization due to progression to pneumonia or febrile convulsion, acute gastroenteritis, or underlying illnesses. Their stool samples were requested to be collected at admission, irrespective of gastrointestinal symptoms. A total of 65 patients submitted their stool samples at 0 to 8 days after the onset of flu symptoms and were included in this study (Table ​(Table1).1). Twelve patients (18.5%) complained of diarrhea during the hospitalization period. All of them were self-limited, and only one patient showed a pathogen, Salmonella group B, in routine stool cultures. This study was approved by the Sanggye Paik Hospital institutional review board. TABLE 1. Demographic characteristics categorized by the presence of viral RNA in stools among the study population hospitalized with pandemic (H1N1) 2009 virus Viral RNA in stool was isolated using the QIAamp virus RNA minikit (Qiagen, Crawley, United Kingdom). Pandemic (H1N1) 2009 virus was detected by two kinds of RT-PCR kits, the Anyplex FluA new H1N1 kit (SeeGene, Seoul, South Korea) and TaqMan Influenza A MGB assays (Applied Biosystems). Pandemic (H1N1) 2009 virus was recovered from stools of 16 patients (24.6%). Nine of them (56.3%) did not complain of any gastrointestinal symptoms during hospitalization. Only 4 patients simultaneously presented diarrhea and fecal excretion of pandemic (H1N1) 2009 virus. Comparing stool pandemic (H1N1) 2009-positive and -negative groups, no difference of frequency was noticed for diarrhea (P = 0.683), nausea (P = 0.746), vomiting (P = 0.898), and abdominal pain (P = 0.977) (Table ​(Table11). The clinical significance and pathophysiology of fecal influenza A virus excretion are not yet clear (1, 9). However, avian influenza A (H5N1) virus has been known to cause severe gastrointestinal manifestations and to replicate in human intestinal tissues (2, 7, 8). To et al. detected pandemic (H1N1) 2009 virus in stool from 4 of 9 patients with positive viral culture from the specimen with the highest viral load (6). This finding suggested the fecal shedding of viable pandemic (H1N1) 2009 virions. In this study, fecal excretion of pandemic (H1N1) 2009 virus was not correlated with the presence of gastrointestinal symptoms as described for avian influenza A (H5N1) virus (7). This study has some limitations: outpatients were not included and virus cultures and quantifications were not performed. However, our data show that considerable numbers of patients shed pandemic (H1N1) 2009 virus in their stool, even in the absence of diarrhea. The frequent detection of fecal pandemic (H1N1) 2009 virus excretion deserves attention in the study of infection control to prevent viral dissemination.