Viral diarrhea in Japanese children: results from a one-year epidemiologic study.

A total of 557 fecal specimens from infants and children with acute gastroenteritis in five places (Maizuru, Tokyo, Sapporo, Saga and Osaka) in Japan from July 2002 to June 2003 were tested for the presence of diarrheal viruses by RT-PCR, PRHA, RNA-PAGE and latex agglutination methods. Of these, 56.4% (314) were found positive for diarrheal viruses. Among them, group A rotavirus was the most prevalent (43.6%, 137 of 314) followed by norovirus (29.9%, 94 of 314), adenovirus (7.6%, 24 of 314), group C rotavirus (6.4%, 20 of 314), sapovirus (5.1%, 16 of 314) and astrovirus (1.6%, 5 of 314), respectively. A high rate (7.4%, 19 of 314) of viral mixed infections, including one triple infection (adenovirus, norovirus and astrovirus) was demonstrated. Norovirus infection that usually has a peak during November and January in Japan was detected year-round and highest in September in our study. Norovirus was subjected to molecular genetic analysis by sequencing. The results clearly indicated that norovirus group II was a dominant genogroup (94.3%, 100 of 106). It is noteworthy that noroviruses detected in this study were classified into 8 genotypes (GI/1, GI/4, GII/2, GII/3, GII/4, GII/5, GII/6 and GII/12). Of these, NVGII/4 was the predominant genotype, followed by NVGII/6, and these presented 75.6% (80 of 106) and 11.3% (12 of 106), respectively. Another interesting feature in our study was the sudden appearance and disappearance of SaitamaU16-like strains belonging to NVGII/6 in the short period (January 2003 to June 2003). Our findings confirmed the presence of many diarrheal viruses co-circulating among Japanese infants and children and showed the great genetic diversity among norovirus.