A study published in this week’s Morbidity and Mortality Weekly Report has found that a new strain of norovirus called GII.4 Sydney was responsible for a majority of the norovirus outbreaks that occurred in the United States from September to December 2012.
According to the data in the study, only 19% of norovirus outbreaks were caused by this strain as of September, but that proportion increased to 58% by December.
“New norovirus strains often lead to more outbreaks— but not always,” said Jan Vinj, PhD, Director of CaliciNet, the company that collected the data, according to a press release. Over the past decade, new strains of GII.4 have emerged about every 2 to 3 years. “We found that the new GII.4 Sydney strain replaced the previously predominant GII.4 strain.”
The issue of MMWR can be found here.