Norovirus outbreaks on the rise with new Sydney strain emerging

January 12th, 2015

Health-care providers and public health practitioners should be vigilant for possible increased norovirus activity in the ongoing season due to an emerging new “Sydney” strain of the virus, the Centers for Disease Control and Prevention reports.

Noroviruses are the leading cause of epidemic gastroenteritis, including foodborne outbreaks, in the United States. Proper hand hygiene, environmental disinfection, and isolation of ill persons remain the mainstays of norovirus prevention and control, the CDC emphasized.

During September–December 2012, a total of 141 (53%) of the 266 reported norovirus outbreaks were caused by GII.4 Sydney, which was first identified in Australia last March. Since then the emergent strain has caused acute gastroenteritis outbreaks in multiple countries. In the United Kingdom, an early onset of the 2012 winter norovirus season was reported in association with emergence of GII.4 Sydney as the dominant strain implicated in outbreaks. In the United States, GII.4 Sydney has spread rapidly nationwide, causing an increasing number of outbreaks.

Most (51%) of the Sydney outbreaks resulted from direct person-to-person transmission; 29 (20%) were foodborne, one (1%) was waterborne. The mode of mission mode was unknown in 39 (28%) of the outbreaks. Long-term–care facilities and restaurants were the most frequently reported settings, accounting for 91 (65%) and 18 (13%) of the GII.4 Sydney outbreaks, respectively. During the three previous winters, the peak in reported norovirus outbreaks occurred in January; therefore, at present, it is too early to make an assessment of the relative magnitude of the current season, the CDC concluded.