Norovirus Outbreaks: Public Health Official Warns of Risk From New Strain

A new strain of norovirus may be circulating, potentially leaving fewer people with immunity, according to Lynn Roberts, an epidemiologist with the Wisconsin Department of Health Services.

Newsweek has reached out to the U.S. Centers for Disease Control and Prevention (CDC), Roberts, and several infectious disease experts for comment and confirmation via email on Saturday morning.

Why It Matters

New strains of viruses are not uncommon, typically arising from mutations or genetic recombination. They can lead to larger outbreaks due to less widespread immunity. The CDC notes that immunity to norovirus after infection is short-term, lasting from a few months to about a year, on average.

The highly contagious illness has reached its highest levels for this time of year in more than a decade, according to the latest CDC data. The CDC has reported 91 outbreaks during the week of December 5, up from an average of 65 during the same period from 2012 to 2020.

“This year the number of reported norovirus outbreaks have exceeded the numbers that we’ve seen recently and in the years before the pandemic,” a spokesperson for the CDC told Newsweek in an email Friday.

The illness causes an average of 900 deaths annually, mostly among older adults, along with 109,000 hospitalizations and 19 million to 21 million cases in the U.S. each year.

What To Know

In an interview with Wisconsin Public Radio on Friday, Roberts, who noted the record high number of infections in the state in December, said, “We’ve had the same kind of dominant strain throughout the country for about 10 years or so, and this year, we have a new one on the scene that’s taking over.”

Norovirus is the leading cause of foodborne illness in the U.S., responsible for nearly 58 percent of foodborne infections annually. A tiny dose of just 10 viral particles can make a person ill, making it one of the most easily transmissible pathogens.

The CDC has identified leafy vegetables, fresh fruits, and shellfish as a common source of norovirus outbreaks. On January 2, the Food and Drug Administration (FDA) issued its fourth oyster recall in three weeks, reflecting an alarming increase in norovirus outbreaks across the nation.

Given the virus is not sensitive to cold temperature and is relatively heat resistant, foods that could be contaminated should be cooked at temperatures higher than 145 degrees Fahrenheit.

What Are Norovirus Symptoms?

Symptoms are often brief but intense, with infected individuals typically experiencing 24 to 48 hours of discomfort, beginning with nausea, vomiting, and followed by diarrhea, among other symptoms.

Most people recover within one to three days, with the exceptions of the elderly, immunocompromised people, and some children. Dehydration is a top concern for sensitive groups.

The majority of the illness is passed through contaminated food and fomites, inanimate objects or surfaces that a contaminated individual touched. The virus can stay on surfaces and objects for several hours, and the CDC encourages people to clean and disinfect surfaces.

The CDC and infectious disease experts recommend washing hands with soap and water, advising against using hand sanitizer, which is less effective because of the virus’ genetic makeup and its interaction with alcohol-based cleaners.

What People Are Saying

Dr. Jatin Vyas, an infectious disease professor at Columbia University Medical School in New York City, told Newsweek in an email Saturday: “I am not aware of any CDC data on the recent uptick in norovirus cases being from a new strain. It is certainly possible and likely…The difference among the strains of norovirus is usually a change in the amino acids used to make up the protein shell on the outside. When this change occurs, the mutated protein folds differently. This change may allow the virus to bind better to its target or evade the immune system.”

He added: “Changes in the viruses occur all of the time. But it is hard to predict whether a change in the norovirus will permit it to become to the dominant circulating strain.”

A spokesperson for the CDC told Newsweek in an email on Friday: “Soap and water work to remove germs from hands, while sanitizer acts by killing certain germs on the skin. Hand sanitizer’s primary active ingredient is alcohol. Alcohol is ineffective against norovirus because the virus’s protective protein shell, called a capsid, prevents the alcohol from penetrating and inactivating the virus.”

What Happens Next

The CDC and doctors urge people to be cautious with potentially contaminated foods and to wash their hands regularly to help curb the rising number of norovirus cases across the U.S.