Molecular epidemiology of Norwalk-like virus (NLV) outbreaks occurring in Kyushu Japan between 1988 and 1993.

In nine outbreaks that occurred in the Kyushu district between 1988 and 1993, we determined the nucleotide sequences of Norwalk-like virus (NLV) gene fragments amplified by RT-PCR and molecular-epidemiologically analyzed the NLV epidemics. It is known that the NLV strains isolated from nine outbreaks of acute gastroenteritis, were divided into five clusters consisting of two genogroups. Described by the year of outbreaks, the genogroup-1 (Norwalk-like virus group) was prevalent in 1988, 1989, and 1992, the genogroup-2 (snow mountain-like virus group) was detected in 1988, 1989, and 1993. Especially it was revealed that various strains of NLV were prevalent in the Kyushu district from 1988 to 1989. Epidemics of the Norwalk-like strain continued to be prevalent in 1992 (FP/7/92), and the strains very close to OSAP 18 continued to be prevalent in 1993 (FP/8/93, FP/9/93). Although the strains belonging to Norwalk virus (KY89) in the genogroup-1 and belonging to P1B (OSAP 18) in the genogroup-2 were detected for a prolonged period from 1988 to 1992/ 1993, the homology in these strains was very close, and this study shows that a high homogeneity was conserved in these strains. It was revealed that various strains of NLV were prevalent in the Kyushu district from 1988 to 1989.

Detection of small round structured viruses in stool specimens from outbreaks of gastroenteritis by electron microscopy and reverse transcription-polymerase chain reaction.

In testing 60 stool specimens small round structured virus (SRSV) particles were detected in 35 (58%) specimens from all 17 outbreaks of gastroenteritis by electron microscopy (EM), while SRSV genes were found in 36 (60%) specimens from 15 outbreaks by reverse transcription-polymerase chain reaction (RT-PCR) by use of 2 primer pairs. Specimens from 2 outbreaks were found SRSV particles-positive by EM but SRSV genes-negative by RT-PCR. EM remains the basic examination method for diagnosis of SRSV agents.

[An epidemic of aseptic meningitis caused by echoviruses in Fukuoka Prefecture during April 1997 to August 1998].

An epidemic of aseptic meningitis in Fukuoka Prefecture during April 1997 to August 1998 was studied to determine the serotype of viruses isolated in Fukuoka Prefecture. In Fukuoka Prefecture, bimodal peaks were seen in July and December 1997. Monthly changes of reported aseptic meningitis patients and period of virus isolation revealed that epidemics of the earlier part in 1997 was caused by echovirus 9 (E 9) and the latter part due to echovirus 30 (E 30). E 9 was isolated mainly in Chikugo Area from June to October 1997 but, E 30 was isolated all in areas of Fukuoka Prefecture. Isolation of E 30 continued after January 1998 in Fukuoka Prefecture. Isolation of echovirus 18 started in June 1998. The main serotypes of isolates are changing. The E 30 isolates are serotyped by neutralization with the aid of antiserum pools for enterovirus type differentiation, but serotyping was difficult with commercially available antiserum. The result of neutralization tests with standard serum and an immune albino rabbit serum prepared in our laboratory with the E 30 isolates indicated that the isolates in Fukuoka Prefecture was an antigenic variant.

Outbreaks of gastroenteritis caused by SRSVs from 1987 to 1992 in Kyushu, Japan: four outbreaks associated with oyster consumption.

From 1987 to 1992, 18 outbreaks of acute non-bacterial gastroenteritis occurred in Kyushu district. The most common symptoms were diarrhea, vomiting, nausea and abdominal cramp. Small round structured viruses (SRSVs) were detected in 52 (44.8%) of 116 stool samples from 17 outbreaks by the electron microscopy (EM) method, and a significant increase in the antibody level was noted in 42 (80.7%) of 52 paired serum samples from 12 outbreaks by the immune electron microscopy (IEM) method and in 18 (51.4%) of 35 samples from 8 outbreaks by the western blot (WB) method. However, according to the WB method, antigen-antibody reaction was not observed to reference antigen strips (SRSV-9/Tokyo 86-510, 63 kDa) in three of the 8 outbreaks. The detected virus was regarded as an etiologic agent for these outbreaks. In four of 5 outbreaks which appeared associated with eating raw oysters, there was a close relation between SRSV infection and consumption of raw oysters.

A mass outbreak of gastroenteritis associated with group C rotaviral infection in schoolchildren.

In 1988, a mass outbreak of epidemic diarrhea, i.e., consisting of 296 cases, occurred in Fukuoka Prefecture. Fecal samples from patients of the outbreak were cultured for bacteria, but all samples were negative. Although direct electron microscopy (DEM) revealed the existence of rotavirus-like particles (diam. 60-70 nm) in the fecal samples, serological studies could not detect any antigenic relation to the ordinary rotaviruses by the reverse passive hemagglutination (RPHA) and enzyme-linked immunosorbent assay (ELISA) tests or immune electron microscopy (IEM) examination. The outbreak appeared to be caused by group C rotaviruses, based on the pattern of electrophoretic migration of RNA genome segments in polyacrylamide gel electrophoresis (PAGE). Furthermore, IEM examination showed large aggregates of virus particles and antibodies when the virus particles were incubated with a reference serum specific for group C rotaviruses.