MOLECULAR EPIDEMIOLOGICAL STUDY ON NOROVIRUS INFECTION IN TWO DISTINCT HOSPITALS IN NORTHEASTERN THAILAND, 2013-2015

Nationwide epidemics due to norovirus (NoV) infections occur periodically in the winter season in the northern hemisphere. NoV outbreaks also have been reported in Thailand. In this study, 564 stool specimens were collected from patients with acute gastroenteritis in northeastern Thailand from October 2013 to May 2015. Partial genome sequences of the N-terminal Shell region of NoVs in the specimens were amplified revealing the majority of NoV cases were detected in samples from December 2013 to February 2014, and from March to April, 2015. The average humidity from December to April is the lowest every year in Thailand, suggesting a possible relationship between the occurrence of norovirus infection and low humidity. Six of 17 GI NoVs were grouped in GI.4 genotype, while 20/30 GII NoVs belonged to GII.4 cluster, of which 19 were closely related to Sydney_2012, a novel GII.4 variant spreading globally since early 2012, while 5/30 GII strains were grouped in GII.17 cluster, which was identified as a new emerging epidemic strain in 2014. The distribution of genogroups and genotypes in NoV in northeastern Thailand was consistent with those of other countries. Economic globalization has increased movements of people among countries so that NoV could easily have been carried into Thailand from other countries.