In the last four months, more than 140 outbreaks in the U.S. have been caused by the new Sydney strain of norovirus. These kinds of contagious bugs cause bouts of diarrhea and vomiting.
The new strain may not be unusually dangerous; some scientists don't think it is. But it is different, and many people might not be able to fight off its gut-wrenching effects.
It often spreads in places like schools, cruise ships and nursing homes. The new strain was blamed for a recent outbreak on the Queen Mary 2.
The Centers for Disease Control and Prevention reported on the new strain Thursday.