Human noroviruses (HuNoVs) are the primary non-bacterial pathogens causing acute gastroenteritis worldwide. Here we reported a co-infection of HuNoVs with different genotypes during an outbreak of gastroenteritis in travelers. The aim was to trace the source and transmission patterns of the infections using next-generation sequencing (NGS). An investigation was conducted on a cross-border travel group who came back to China from Thailand for symptoms of gastroenteritis. Anal swabs were collected from 23 people and samples were analyzed using RT-qPCR. A total of 11 samples tested positive for HuNoVs. All samples tested negative for bacterial pathogens in the surveillance list. Positive samples for HuNoVs were further analyzed using NGS. Seven out of 11 positive samples were sequenced and 16 viral genome sequences for 10 different strains of HuNoVs were obtained. We demonstrated that the outbreak was associated with co-infection of multiple genotypes of HuNoVs and the source of infections was probably contaminated water or food. Besides, four different HuNoVs genotypes (GI.5[P12], GIX.1[GII·P15], GI.7[P7] and GII.8[P8]) were identified in one patient. Co-infection with both genogroup GI and GII, and co-infection with two different P types ([P10] and [P13]) of genotype GI.3 were identified in different patients. Findings from this study show that individuals can be simultaneously infected with multiple strains of HuNoVs and NGS can help investigating these issues. Further, this study shows that food and water are potential vehicles for transmission of multiple foodborne viruses.
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