Outbreak of human astroviruses 1 and Melbourne 2 in acute gastroenteritis pediatric patients in Japan during the COVID-19 pandemic, 2021.

BACKGROUND: Human astrovirus (HAstV) infection is one of the leading causes of acute gastroenteritis in young children. The present study reports the outbreak of HAstV in children with acute gastroenteritis in Kyoto, Japan, during the COVID-19 pandemic, 2021. METHODS: A total of 61 stool samples were collected from children with acute gastroenteritis who visited a pediatric outpatient clinic in Maizuru city, Kyoto, Japan from July to October, 2021. HAstV was screened by RT-PCR, and the genotypes were identified by nucleotide sequence analysis. RESULTS: Of 61 cases of acute gastroenteritis, 20 were mono-infected with HAstV alone. In addition, mixed infection of HAstV and NoV, and HAstV and RVA were also detected in 15 and 1 cases, respectively. Of 36 HAstV strains detected in this outbreak, 29 and 7 were HAstV1 and MLB2 genotypes, respectively. All HAstV1 strains were closely related to the HAstV1 reported from Thailand and Japan in 2021 and all of them belonged to subgenotype HAstV1a. Among MLB2, they were most closely related to the MLB2 strains reported from China in 2016 and 2018. CONCLUSIONS: After the kindergartens and schools were re-opened at the middle of 2021 in Japan, an outbreak of HAstV was reported. Control measures against the COVID-19 pandemics might affect the spread of diarrheal virus infection. Here we report the outbreak of HAstV1 and MLB2 in Kyoto, Japan, during COVID-19 pandemic in 2021.

Emerging norovirus GII.4 Sydney[P31] causing acute gastroenteritis outbreak in children in Japan, during COVID-19, 2021.

INTRODUCTION: Norovirus (NoV) is the most common agent causing outbreaks and sporadic cases of acute gastroenteritis among all ages, especially children under 5 years old. During the coronavirus disease 2019 (COVID-19) pandemic, NoV infection has decreased drastically in Japan due to school closures and no outbreak related to NoV infection had been reported. METHOD: In mid-September 2021, NoV outbreak occurred in kindergarten and nursery schools in Maizuru, Kyoto prefecture, Japan. Twenty-six stool samples collected from patients who were diagnosed of NoV gastroenteritis from the outbreak by an immunochromatographic (IC) kit at a pediatric outpatient clinic in Maizuru city during 3 weeks from September 13 to October 8, 2021 were examined for the presence of NoV GII by reverse transcriptase-polymerase chain reaction (RT-PCR), genome sequencing, and phylogenetic analysis. RESULT: All 26 samples were confirmed positive to NoV GII and their genotypes were identified as GII.4 Sydney[P31]. The amino acid substitutions in open reading frame1 (ORF1) and ORF2 genes were found when compared with previously detected sporadic NoV GII.4 Sydney[P31] strains isolated in Japan. The clinical characterization of infected children was described. Most of the children were mild cases and vomiting was the most frequent clinical symptom. CONCLUSION: This study reported a recent emergence of NoV GII.4 Sydney[P31] causing acute gastroenteritis outbreak in children in Japan during the COVID-19 pandemic and suggests a need for further monitoring of NoV GII.4 variants.