From Our 2013 Archives
New Strain of Norovirus Spreading Quickly in U.S.
By Salynn Boyles
Reviewed by Laura J. Martin, MD
Jan. 24, 2013 -- The flu is not the only highly contagious disease raging this winter.
A new strain of norovirus is causing intestinal illness outbreaks across the country, the CDC confirmed today.
Norovirus is often to blame when large numbers of people get sick on cruise ships or in schools, nursing homes, and other places where people live, work, or play in close quarters.
CDC officials also reported a rise in outbreaks of sickness caused by drinking raw milk.
The findings appear in the Jan. 25 issue of the Morbidity and Mortality Weekly Report.
New Norovirus Spread Quickly
The new norovirus strain was first identified in Australia in March of last year, and it had spread across the United States by year's end.
Of the 266 norovirus outbreaks reported during the last four months of 2012, 141 involved the Australian strain. During this time, outbreaks caused by it rose from 19% to 58%.
Sickness from norovirus is often called "food poisoning," but the highly contagious virus can also be spread by water, person-to-person contact, or simply by touching an infected object.
Outbreaks can happen anytime, but they are most common in the winter months.
Cruise Ship Outbreak Involved New Strain
A norovirus outbreak late last week that involved 300 children at an Arkansas middle school was not caused by the newer strain. But one that happened during a Christmas sailing of the luxury cruise ship Queen Mary 2 was, says Jan Vinje, PhD, who heads the National Calicivirus Laboratory at the CDC.
CDC epidemiologist Aron Hall says it may not be clear for several months if more people are getting sick or more outbreaks are occurring as a result of the new strain.
"We see new strains emerge every few years and sometimes they are associated with increased disease activity," he says. "We certainly want people to be aware that this potential exists, but the mainstays of norovirus prevention are still the most important things people can do to protect themselves."
He suggests these strategies to prevent infection:
23 Food-borne Illness Deaths in 2009, 2010
A separate report on food-borne disease outbreaks in 2009 and 2010 showed a decline in such outbreaks, but CDC epidemiologist Hannah Gould, PhD, says the drop was largely due to a new way of reporting the illnesses that excluded many norovirus cases.
There were 1,527 food-borne illness outbreaks reported to CDC during the two-year period, resulting in nearly 29,500 illnesses, 1,184 hospitalizations, and 23 deaths.
Beef, dairy, fish, and poultry were associated with the largest number of outbreaks, but eggs made more people sick than any other single food.
A large salmonella outbreak in 2010 led to the recall of more than half a billion eggs and sickened about 2,000 people across the country.
Other foods implicated in multi-state outbreaks during the reporting period included alfalfa sprouts, ground turkey, ground beef, unpasteurized cheeses, hazelnuts, and cookie dough.
Raw Milk Outbreaks Increasing
Gould says dairy joined the list of foods that caused the most illness for the first time in years, due to a growing number of outbreaks caused by unpasteurized dairy products.
Sixty percent of states allow the sale of raw milk in some form, according to a 2011 survey by the National Association of State Departments of Agriculture.
Last year, another group of CDC researchers reported that raw milk is 150 times more likely to cause illness than pasteurized milk.
Contamination with campylobacter bacteria is responsible for most illnesses linked to raw milk and the foods made from it.
Seventeen campylobacter outbreaks that were traced to unpasteurized dairy products were reported in 2009 and 2010.
Gould says food-borne illness is often preventable if people remember to:
SOURCES: Barclay, L., and Gould, H. Morbidity and Mortality Weekly Report, Jan. 25, 2013.Hannah Gould, PhD, epidemiologist, CDC.Jan Vinje, PhD, director, National Calicivirus Laboratory, Division of Viral Diseases, CDC.Aron Hall, DVM, Division of Viral Diseases, National Center for Immunization and Respiratory Diseases, CDC.News release, CDC.Food Safety News: "Norovirus update, Jan 24, 2013."NBC News: "Passengers on Queen Mary Sickened by Unidentified Pathogen."