Those summer colds are the worst: New strain of a stomach virus circulating around the United States.. The CDC says that GII.4 Sydney is the leading cause of outbreaks in the US .. it can be confused with the flu, it causes severe vomiting and diarrhea.. According to the CDC, about 51% of the cases in the U.S. were caused by person-to-person transmission and 20% resulted from contaminated food..
