A new strain of norovirus first detected in Australia last March is causing outbreaks in the United States and other countries, officials say.
Researchers at the Centers for Disease Control and Prevention in Atlanta analyzed data from last year collected through CaliciNet on norovirus strains associated with outbreaks in the United States.
The CDC found of the 266 norovirus outbreaks reported during the last four months of 2012, 141 were caused by the new strain called GII.4 Sydney.
"The new strain spread rapidly across the United States from September to December," Dr. Aron Hall, an epidemiologist at CDC's Division of Viral Diseases, said in a statement. "The proportion of reported outbreaks caused by this strain increased dramatically from 19 percent in September to 58 percent in December."
Norovirus -- also referred to as stomach flu although it has nothing to do with influenza -- is very contagious and is the top cause of acute gastroenteritis, which leads to diarrhea and vomiting.
Each year, more than 21 million in the United States get infected and develop acute gastroenteritis; approximately 800 die, with young children and the elderly at the highest risk, Hall said.
Norovirus spreads primarily from infected people to others via direct contact, contaminated food, water and surfaces.
Dr. Jan Vinje, director of CaliciNet, said over the past decade, new strains of GII.4 have emerged about every two to three years.
The best ways to help prevent norovirus include: washing hands with soap and water, disinfecting surfaces, rinsing fruits and vegetables, cooking shellfish thoroughly, and not preparing food or caring for others while ill.
The findings were published in the CDC's Morbidity and Mortality Weekly Report.
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