A new strain of norovirus, which causes diarrhea and vomiting, has been identified in the United States.
This new strain spread rapidly across the nation. It was was the leading cause of norovirus outbreaks from September to December, according to the Centers for Disease Control and Prevention.
The proportion of reported outbreaks caused by this strain increased from 19 percent in September to 58 percent in December.
Norovirus, sometimes called cruise ship disease, is extremely contagious. The disease sickened more than 200 people who attended a cheerleading competition in Everett in February last year.
Each year, more than 21 million people in the United States become ill from the disease and approximately 800 die. Young children and elderly adults have the highest risk for severe illness.