Virological, serological, and clinical features of an outbreak of acute gastroenteritis due to recombinant genogroup II norovirus in an infant home.

Norovirus (NV) is an important cause of acute nonbacterial gastroenteritis worldwide. Recently, several sporadic cases due to naturally occurring recombinant NVs have been reported. In January 2000, there was an outbreak of gastroenteritis in an infant home in Sapporo, Japan. Of 34 residents of the home that were less than 2 years old, 23 developed gastrointestinal symptoms and NV infection was confirmed by conventional reverse transcription-PCR to detect the RNA polymerase region of genogroup II NV. In this virus, the RNA polymerase region shared 86% nucleotide identity with Hawaii virus but only 77% with Mexico virus; however, its capsid region shared only 70% identity with Hawaii virus but 90% with Mexico virus. On the other hand, both regions shared a higher 96% nucleotide identity with Arg320 virus, which was found in Mendoza, Argentina, in 1995 and considered to be a recombinant of Hawaii and Mexico viruses. The findings indicate that the virus involved in the outbreak was similar and may have evolved from the Arg320 virus. Clinically the cases were more severe than those of previously reported sporadic or outbreak cases of NV infection.

Detection and differentiation of Norwalk virus by reverse transcription-polymerase chain reaction and enzyme-linked immunosorbent assay.

We have developed a reverse transcription-polymerase chain reaction and enzyme-linked immunosorbent assay (RT-PCR-ELISA), using genetic cluster-specific probes in a microtiter plate format, for the detection and differentiation of Norwalk virus (NV) in stool samples. The specificity of the RT-PCR-ELISA was confirmed by testing 76 stool specimens and 15 tissue culture fluids derived from growths of unrelated viruses. The sensitivity of the RT-PCR-ELISA was compared with conventional PCR and Southern hybridization by testing the four cDNA clones derived from the RNA-dependent RNA polymerase region of the NV68 (NV/GI) virus and viruses in the NV/GII/P1B, the NV/GII/P2A, and the NV/GII/P2B cluster. This assay was as sensitive as the conventional RT-PCR with Southern hybridization regardless of primer pairs and probes used in the experiments. However, the actual sensitivity of this method was higher when clinical stool samples were examined because this assay examines all the samples irrespective of the RT-PCR results. The RT-PCR-ELISA format is simple, time saving, and suitable for testing many samples. It should be reliable for large-scale epidemiological studies of NV.