Rotavirus infection is a serious gastrointestinal 
infection that is usually prevalent during winter months and often 
seen in infants and young children. Studies on genotypes of 
prevalent rotavirus strains are quite important for preventing 
infection, developing vaccines, and its evaluation. We 
investigated the characteristics of rotavirus infections of Nasu 
Region of Tochigi, Japan and to compare to the other region 
before introduction of rotavirus vaccines. We examined the 
clinical findings in 147 patients and analyzed the clinical findings 
of the 37 patients with a fecal sample positive for rotavirus 
antigen. Furthermore, viral genotypes were determined using 
rotavirus-positive samples from 27 of these 37 patients. The 
genotypes were determined as G1P [8] in 5 samples, G3P [8] in 5 
samples, G9P [8] in 3 samples, and G6P [9] in 2 samples. We 
were able to analyze the phylogenetic trees of these genotypes. Of 
particular note, we detected G6P [9] which were extremely rare in 
human beings but common in cattle. It was suggested that the 
rates of hospitalization due to rotavirus infections of infants from 
6 to 11 months of age would be reduced by 42% when the 
vaccination coverage rates increase to 50% in Japan. Studies on 
changes in prevalent strains after vaccine introduction need to be 
conducted.