What to know about rising outbreaks of norovirus, the gastrointestinal ailment

Cases of the illness known as norovirus - which induces miserable bouts of vomiting and diarrhea - are surging across the United States, according to the Centers for Disease Control and Prevention. Ninety-one outbreaks of the gastrointestinal bug were reported the week of Dec. 5, the latest period for which data is available. That’s 22 more outbreaks than in the last week of November.

While sometimes referred to as the stomach flu, the disease is not caused by the influenza virus, which results in respiratory illness.

There are about 2,500 reported outbreaks each year in the United States, happening most frequently between November and April. When new strains of norovirus emerge, case counts usually rise, according to disease trackers.

“This year, the number of reported norovirus outbreaks have exceeded the numbers that we’ve seen recently and in the years before the pandemic,” according to the CDC.

The World Health Organization reports that globally norovirus spawns an estimated 685 million cases annually, including 200 million cases among children younger than age 5.

Experts say the surge can be linked to the fall and winter seasons, when people are indoors more and are gathering for the holidays. It also reflects reduced immunity after periods without outbreaks, notably during the coronavirus pandemic, when people traveled less and were especially vigilant about hand-washing.

The good news: After a year with spiking cases, outbreaks tend to decline in subsequent periods.

What are the symptoms of norovirus?

Norovirus is highly contagious and causes vomiting and diarrhea, which can lead to dehydration. Symptoms of dehydration include decreased urination, dry mouth and feeling dizzy when standing up. People may experience fever, headaches and body aches.

The virus can infect anyone, but like many other viral illnesses, young children and older adults are more prone to significant symptoms.

What is the incubation period for norovirus?

The incubation period for a norovirus infection ranges from 12 to 48 hours. This means that a person may not show any symptoms right after being infected because the virus can take time to manifest. The exact timing varies depending on factors such as overall health and the immune response of an infected person. Some people may show symptoms sooner than the typical 12- to 48-hour window, but others might not notice them until later in the incubation period.

How does the virus spread?

The virus spreads through direct contact with an infected person, such as sharing food. Norovirus can also spread through contaminated food and water. If vomit or fecal particles are present and a person touches them, the person can become infected.

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How long is norovirus contagious?

Most infected people start to recover in one to three days, but they can still transmit the virus for two weeks or longer after feeling better.

These measures can help stem spread of the disease: frequent hand-cleaning, washing laundry in hot water and staying home for 48 hours after symptoms have stopped to prevent spreading a norovirus infection.

“Staying home is particularly important if you’re working in a school, day care or with elderly people, as they are particularly prone to developing severe disease,” according to Daniel R. Kuritzkes, chief of infectious diseases at Brigham and Women’s Hospital in Boston.

Is norovirus deadly?

Norovirus is usually not life-threatening, especially in the United States and other high-income nations. For most people, the infection clears up within a few days. Deaths from the ailment are rare in the United States, but each year, 900 people, mostly 65 and older, die of the disease. These are usually people with significant underlying medical conditions.

Annually, there are about 109,000 hospitalizations and 465,000 emergency department visits in the United States blamed on the norovirus, and most of the patients are young children. Children account for most of the nearly 2.3 million outpatient visits each year.

In low-income countries, norovirus exacts a far steeper toll, according to the WHO: The 200,000 deaths each year worldwide, including 50,000 child deaths, are concentrated in those nations.

“Severe disease is more likely to be lethal in lower-income countries because people have limited access to emergency medical care,” Kuritzkes said.

How do you treat norovirus?

There is no treatment specifically for a norovirus infection. Instead, recovery entails rest and drinking ample fluids. For small children and babies who cannot drink fluids, intravenous hydration may be recommended if they become dehydrated.

No approved norovirus vaccines exist. Several are being tested in clinical trials worldwide, but developing one has been challenging.

“It may be like the common cold that there are so many strains, so it might be hard to make a vaccine,” said Robert Legare Atmar, an infectious-diseases specialist at Baylor College of Medicine. “Some clinical studies have shown that a vaccine can be effective in adults, but whether we can do that in young children remains to be seen.”

What should you eat if you have the virus?

Health experts recommend minimizing solid foods during a norovirus infection and advise focusing on liquids such as sports drinks and broths - but not beverages filled with sugar, because they can worsen diarrhea, according to the Mayo Clinic. Doctors also advise cutting out dairy products such as milk and cheese.

When it’s time to reintroduce solids, start with bland foods in small but frequent portions.