Genotypes and Clinical Manifestations of Sapovirus-Associated Gastroenteritis in Mie Prefecture, Japan, 2010–2022

Tomoichiro OKA, National Institute of Health Sciences

Hajime KUSUHARA1, Yen Hai DOAN2, Akihito KOBAYASHI1,3, Hirotaka TAKAGI2, Tomoichiro OKA2,4 1 Mie Prefecture Health and Environment Research Institute, Mie, Japan 2 National Institute of Infectious Diseases, Japan Institute for Health Security, Tokyo, Japan 3 Mie Prefectural Tsu Health Center, Mie, Japan 4 National Institute of Health Sciences, Kanagawa, Japan

Molecular Epidemiology & Evolution

Sapovirus is one of the major viruses causing acute gastroenteritis in children. To investigate its long-term prevalence, genetic diversity, and clinical characteristics, we analyzed 1,981 fecal specimens collected through sentinel pediatric acute gastroenteritis pathogen surveillance in Mie Prefecture, Japan, from 2010 to 2022. Norovirus and sapovirus were detected in 521 (26.3%) and 236 (11.9%) specimens, respectively. Annual sapovirus detection ranged from 6.9% to 17.5%, occasionally exceeding that of norovirus. Among the 236 sapovirus-positive cases, 221 were genotyped, identifying nine genotypes—most commonly GI.1 (36.7%), GII.3 (16.7%), and GII.1 (12.2%). Phylogenetic analysis of near full-length sequences showed that these three major genotypes formed distinct clusters by year of detection, suggesting continuous genetic changes within the same genotype. The main clinical manifestations among sapovirus-positive patients were diarrhea (68.2%) and vomiting (61.4%), with a higher frequency of vomiting in children over 3 years of age. Fever (12.7%) and respiratory symptoms (14.2%) were also observed. Frequent coinfections with other viruses (25%) highlight the need for comprehensive diagnostic approaches. Reinfections with different genotypes were identified in five patients, indicating genotype-specific immune responses. To evaluate viral genome stability and infectivity, 80 sapovirus-positive samples stored at 4°C for up to six years were reanalyzed. Sapovirus genome was detected in 86.3% by metagenomic analysis, although no virus could be propagated in culture. This study clarified the prevalence of viral genotypes as well as clinical findings of sapovirus-positive gastroenteritis in children and revealed trends by age.