Norovirus is a stomach bug that causes diarrhea and vomiting and a new strain was responsible for most outbreaks of the disease in the U.S. in recent months, the Centers for Disease Control and Prevention announced Thursday.
Last fall, 53 percent of norovirus outbreaks were caused by this new strain, GII.4 Sydney. The CDC says, between September and December, the proportion of norovirus outbreaks caused by the new strain increased from 19 percent to 58 percent.
Norovirus illnesses are typical this time of year and peak usually in January. Therefor, it's still too soon to tell if the new strain will cause more outbreaks this season than in the past.
“New norovirus strains often lead to more outbreaks but not always,” said Dr. Jan Vinjé, director of CaliciNet, the CDC's surveillance system for norovirus.
Norovirus is very contagious. Every year about 21 million people in the U.S. fall ill from the bug, and about 800 die. Young children and the elderly are at highest risk for severe illness, the CDC said.
According to the CDC, fifty-one percent of outbreaks caused by the new strain were spread person to person, 20 percent were due to foodborne illness, 1 percent due to waterborne illness, and 28 percent had an unknown mode of transmission.
The best ways to prevent norovirus infections are hand washing with soap and water; disinfecting surfaces; rinsing fruits and vegetables; cooking shellfish thoroughly; and not preparing food or caring for others while ill, the CDC said.