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CDC calls attention to new strain of norovirus


A new strain called GII.4 Sydney was the leading cause of norovirus outbreaks in the United States from September to December, according to a study by the Centers for Disease Control and Prevention.

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

“The new strain spread rapidly across the United States from September to December 2012,” Aron Hall, DVM, MSPH, epidemiologist in the CDC’s Division of Viral Diseases, said in a news release. Hall said the proportion of the strain in reported outbreaks increased from 19% to 58% during that time frame.

Norovirus in the U.S. is the leading cause of acute gastroenteritis, which affects more than 21 million people a year and causes about 800 deaths. Young children and elderly adults have the highest risk for 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, with activity usually peaking in January.

“New norovirus strains often lead to more outbreaks, but not always,” said Jan Vinjé, PhD, director of CaliciNet. Over the past decade, new strains of GII.4 have emerged about every two to three years. “We have found that the new GII.4 Sydney strain replaced the previously predominant GII.4 strain,” Vinjé added.

Health professionals should remain vigilant to potential increases in norovirus infection this season due to GII.4 Sydney, according to the CDC. They should follow standard prevention and control measures for norovirus. The best ways for everyone 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,” Hall said. The CDC “continues to work with state partners to watch this closely and see if the strain is associated with more severe illness.”

Better surveillance in the United States and abroad have helped to detect new strains of norovirus sooner, according to the CDC. Early identification of new strains helps to alert the public and health professionals to better prevent infections and control outbreaks.


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