Y-027. Molecular Epidemiology of Noroviruses in Singapore, 2006-2007
Background: Noroviruses are a major cause of viral gastroenteritis outbreaks worldwide. They are a significant problem in closed settings such as long-term care facilities and schools. Singapore experienced a surge in norovirus outbreaks in 2006-2007. As the molecular epidemiology of noroviruses in Singapore had never previously been studied, this study aimed to determine the genetic composition of norovirus strains detected during this period and to characterize them by sequencing. Methods: Stool samples from 8 outbreaks from August 2006 to January 2007 were studied. In addition, positive norovirus samples from sporadic cases during this period were also included in the analysis. Extracted RNA from stool samples was first tested by real-time reverse-transcription PCR (RT-PCR) for norovirus and to determine genotype. RNA from positive samples was then amplified with primers specific to the capsid N terminus/shell (N/S) gene by RT-PCR. The amplicons were sequenced, the sequences were edited and phylogenetic analysis was performed. Results: The outbreaks were from 5 nursing homes, 2 schools and 1 hospital. There were 24 positive samples from the outbreaks (all adults) and 3 from sporadic cases (all children). All positive strains were typed as Genotype II, subgroup 4. Based on phylogenetic analysis, all 27 strains were closely related to genotype II/4 2006b variant that appeared in Europe at the end of 2005. Conclusions: A new emerging variant of the GII/4 norovirus group was the cause of norovirus outbreaks and sporadic cases in Singapore from August 2006 to early 2007. This finding is similar to other findings reported in Europe, USA and Hong Kong during this period and suggests the rapid worldwide epidemic spread of new variants of norovirus.