A new strain of the norovirus gastrointestinal infection called GII.4 Sydney is spreading quickly and caused 58% of norovirus outbreaks in December, up from 19% of norovirus outbreaks recorded for September, according to the Centers for Disease Control and Prevention.
Of the 266 norovirus outbreaks reported during the past four months of 2012, 141 were caused by the GII.4 Sydney strain, according at data collected by CaliciNet, a network of participating public health and food regulatory labs.