Abstract:
Human norovirus (HuNoV) is a major cause of acute gastroenteritis and affects people of all ages worldwide. Symptoms include vomiting and watery diarrhea. Outbreak of HuNoV infection often occurs in schools, hospitals, ships, and in close-contact settings. There is currently no vaccine or therapy available for HuNoV infection because there are multiple circulating strains. Therefore, HuNoV reinfection in the same individual is possible over the lifetime. The predominance of HuNoV has been observed to change every 2 4 years and the most common strain currently circulating is GII.4 Sydney 2012. To assess the HuNoV strains circulating in Thailand between 2015 and 2016, we screened 1,391 stool samples obtained from hospitalized patients with diarrhea. Stool samples were analyzed for HuNoV by RT-PCR, nucleotide sequencing, and phylogenetic analysis. We found HuNoV among 184 (13.2%) stool samples, which consisted of 35% GII.4, 13% GII.17, 9% GII.P12/GII.3, 36% GII.P16/GII.2 and 7% of other strains (GII.7, GII.15, GII.16, GII.P7/GII.6, GII.P7/GII.14 and GII.P16/GII.4). GII.17 strain was detected from September 2015 to December 2016, but did not replace GII.4 to become the major HuNoV. In addition, there were major outbreaks of HuNoV at the end of 2016 in Thailand in which GII.P16/GII.2 was the major outbreak strain. In summary, evidence suggests an epidemiological shift from the previously more common GII.4 Sydney 2012 to the GII.P16/GII.2 strain. Given past HuNoV outbreaks in primary schools, it is important to monitor HuNoV strains in circulation to better contain potential future outbreaks in the community.