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CDC Report: New Norovirus Strain Causing Most Norovirus Outbreaks in U.S.

Not yet known whether strain will cause more outbreaks than previous years (Jan. 25)

A new strain of norovirus called GII.4 Sydney was the leading cause of norovirus outbreaks in the U.S. from September to December 2012, according to a new study published by the Centers for Disease Control and Prevention (CDC) in Morbidity and Mortality Weekly Report. The new strain was detected in Australia in March 2012, and caused outbreaks in that country and several other countries.

CDC researchers analyzed 2012 data on norovirus strains associated with outbreaks in the U.S. They found that of the 266 norovirus outbreaks reported during the last 4 months of 2012, 141 (53%) were caused by the GII.4 Sydney strain.

Norovirus is extremely contagious. In the U.S., norovirus is the number one cause of acute gastroenteritis, which leads to diarrhea and vomiting. Each year, more than 21 million people in the U.S. are infected and develop acute gastroenteritis, and approximately 800 die. Young children and elderly adults have the highest risk of severe illness.

Norovirus spreads primarily from infected people to others through direct contact. It also spreads through contaminated food, water, and surfaces. Most outbreaks occur from November to April, and activity usually peaks in January.

According to the CDC, healthcare professionals should remain vigilant to potential increases in norovirus infection this season due to GII.4 Sydney, and they should follow standard prevention and control measures for norovirus. In addition, the public should know that the best ways to help prevent norovirus infection 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.

“Right now, it’s too soon to tell whether the new strain of norovirus will lead to more outbreaks than in previous years. However, CDC continues to work with state partners to watch this closely and to see if the strain is associated with more severe illness,” said Dr. Aron Hall, epidemiologist in the CDC’s Division of Viral Diseases.

Source: CDC; January 25, 2013.

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