New Strain of Norovirus Is Circulating in the U.S.

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Piggybacking off this year’s influenza epidemic, a new strain of the highly contagious norovirus has reached the U.S. from Australia.

The U.S. Centers for Disease Control and Prevention (CDC) reports in the Morbidity and Mortality Weekly Report that the new norovirus strain, called GII.4 Sydney, is currently the leading cause of norovirus outbreaks in the U.S. and accounted for 58% of cases of the infection in December.

Often confused with the stomach flu because of its contemporaneous circulation with influenza during winter months, norovirus causes 21 million cases of illness, often involving severe vomiting and diarrhea; 70,000 hospitalizations each year in the U.S.; and 800 deaths. While influenza is a respiratory illness, norovirus, which comes in five forms, favors the stomach and intestinal tract, causing inflammation of tissues that leads to pain, nausea, as well as diarrhea and vomiting. According to the CDC, about 51% of the cases in the U.S. were caused by person-to-person transmission and 20% resulted from contaminated food. Most infections occur in places where large numbers of people are gathered, such as schools, nursing homes and cruise ships, where the virus can pass easily from host to host.

(MORE: Norovirus Outbreak: Why You Shouldn’t Keep Your Grocery Bag in the Bathroom)

The new strain of norovirus was first identified in March 2012 in Australia and has since sickened people on several continents. Historically, the GII strains have caused more severe illness than other versions of the virus, but officials at the CDC says it is too early in the season to determine if GII.4 Sydney is infecting people at higher rates than in previous years. The norovirus season runs from November through March and cases typically peak in January.

“Although most of the time you recover after 24 or 48 hours, [norovirus] is a reason for people to come to the emergency room and is even responsible for a small number of death each year. It’s not a completely innocuous virus and can certainly ruin a vacation,” says Dr. John Treanor, chief of the Infectious Diseases Division at the University of Rochester Medical Center.

There are no treatments for norovirus, other than riding out the infection, but Treanor and a group of scientists are currently testing a vaccine developed by LigoCyte Pharmaceuticals. The shot contains a part of the norovirus’ outer layer, which they hope will generate a strong immune response in those who get immunized.

(MORE: Bad Food: Illnesses from Imported Food are on the Rise, CDC Says)

A vaccine would be critical for preventing the disease from escalating in populations; because it spreads so quickly, norovirus infections are difficult to contain. “You really only have to be exposed to a couple of viral particles to get sick,” says Treanor. “This makes it very contagious because when you have norovirus, you are dispersing literally millions of particles. When it only takes one or two to make the next person sick, it translates into very high contagiousness.”

Fortunately, the same things you do to protect yourself from flu also work in holding off infection with norovirus. The CDC recommends the following:

  • Wash your hands carefully with soap and water, especially after using the bathroom or changing diapers and before handling food.
  • Carefully wash produce and seafood before cooking and consuming them.
  • If you’re sick, wait two to three days after you recover before preparing food for anyone.
  • Immediately clean any infected or contaminated surfaces and wash laundry thoroughly.