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

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Story Created: Jan 25, 2013 at 10:58 AM PDT

Story Updated: Jan 25, 2013 at 10:58 AM PDT

(CDC news release) A new strain of norovirus called GII.4 Sydney was the leading cause of norovirus outbreaks in the United States from September to December 2012, according to a study published in Morbidity and Mortality Weekly Report released this week by the Centers for Disease Control and Prevention.

According to a CDC news release:

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 collected through CaliciNet on norovirus strains associated with outbreaks in the United States. 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,” said Dr. Aron Hall, epidemiologist, CDC’s Division of Viral Diseases (DVD). “The proportion of reported outbreaks caused by this strain increased dramatically from 19 percent in September to 58 percent in December.”

Norovirus is very contagious. In the United States, norovirus is the number one cause of acute gastroenteritis, which leads to diarrhea and vomiting. Each year, more than 21 million people in the United States get infected and develop acute gastroenteritis; approximately 800 die. 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. Norovirus infections are common during this time of the year. Most outbreaks occur from November to April, and activity usually peaks in January.

“New norovirus strains often lead to more outbreaks but not always,” said Dr. Jan Vinjé, director of CaliciNet. Over the past decade, new strains of GII.4 have emerged about every 2 to 3 years. “We found that the new GII.4 Sydney strain replaced the previously predominant GII.4 strain.”

Read the entire CDC news release HERE.