Epidemiology and molecular characteristics of norovirus GII.4 Sydney outbreaks in Taiwan, January 2012-December 2013

In 2012, a new norovirus GII.4 variant (GII.4 Sydney) emerged and caused the majority of the acute gastroenteritis outbreaks in Australia, Asia, Europe, and North America. We examined the epidemiologic and molecular virologic characteristics of reported acute gastroenteritis outbreaks determined to be caused by norovirus in Taiwan from January 2012 to December 2013. A total of 253 (45.7%) of 552 reported acute gastroenteritis outbreaks tested positive for norovirus, of which 165 (65.5%) were typed as GII.4 Sydney. GII.4 Sydney outbreaks were reported from all geographic areas of Taiwan and occurred most frequently in schools (35.8%) and long-term care facilities (24.2%). Person-to-person transmission was identified in 116 (70.3%) of the outbreaks. Phylogenetic analyses of full-length ORF2 of eight specimens indicated that GII.4 Sydney strains detected in Taiwan were closely related to strains detected globally. Continued outbreak surveillance and strain typing are needed to provide information on epidemiologic and virologic trends of novel norovirus strains.