‘California is buzzing with norovirus,’ expert says. What to know about stomach flu spread

Norovirus is on the rise overall in the United States, federal officials say, even as the West sees a slight dip in reported cases.

After peaking in January, cases of the virus were steadily dropping in the western part of the country — including California, Nevada and Oregon — as of Feb. 10, the Centers for Disease Control and Prevention said.

Norovirus is a contagious virus that’s sometimes referred to as food poisoning or the stomach flu, according to the California Department of Public Health.

The rise in norovirus cases aren’t completely out of the ordinary, said Dr. Peter Chin-Hong, professor and doctor specializing in infectious disease at UC San Francisco.

“It’s just like RSV and all these other things where we didn’t see a lot in the beginning of the (coronavirus) pandemic, and then we’re making up for lost time,” Chin-Hong said. “Last year, we also had a lot of norovirus.”

According to the CDC, outbreaks of the virus commonly occurs in the late fall, winter, and early spring.

Chin-Hong said the virus typically peaks in the winter.

What is norovirus? What are the symptoms?

“Norovirus is the leading cause of vomiting and diarrhea” in the United States as well as foodborne illness, the CDC said on its website. “People of all ages can get infected sick with norovirus, which spreads very easily and quickly.”

Unlike respiratory viruses, such as influenza or COVID-19, norovirus affects the gut.

Symptoms of the virus include projectile vomiting, abdominal pain, fever and flu-like symptoms.

How is stomach flu treated?

According to the CDC, there is no specific medicine to treat norovirus.

If you get sick with the stomach flu, the agency advises you to drink plenty of fluids or sports drinks to avoid dehydration.

The Mayo Clinic said a doctor may recommend medication to treat diarrhea and nausea.

Typically, the illness should resolve within a few days.

How is the virus spread?

Norovirus is typically spread by direct contact with someone who is sick with norovirus, consuming foods or drinking beverages that are contaminated or touching a contaminated surface and putting unwashed hands into the mouth.

It can spread quickly in closed and crowded spaces, such as cruises and schools, the department said.

“If you have a lot of people crowded together, you just have a statistically higher chance of getting infected,” Chin-Hong said. “Not because people are breathing on each other but there’s likely going to be shared surfaces and utensils and people touching things and then touching their nose and mouth.”

Are norovirus cases on the rise in California?

Norovirus cases have been climbing in the California region since November, peaking in January, the CDC reported.

In January, the state issued a warning about oysters imported from Mexico that are potentially contaminated with the virus.

“California is buzzing with norovirus right now,” Chin-Hong said.

However, he said, many people sickened by the norovirus may not get tested for it because that test isn’t commonly administered.

Experts get a better understanding of norovirus case trends by looking at wastewater studies along with postivity tests, he said.

According to the California Department of Public Health, norovirus causes about 19 to 21 million cases of acute gastroenteritis each year nationwide.

In 2022, Calfiornia saw up to 2,520,000 reported or projected cases of norovirus-related illness and 108 deaths, according to the 2024 California State of Public Health Report.

“Basically, what we see in the hospital and from test positivity is just the tip of the iceberg because many people are not testing,” Chin-Hong said.

He anticipates that the virus will continue to trend downward as the weather gets warmer.

How to avoid norovirus-related illness

Washing your hands with soap and water can help you avoid getting sick with norovirus, Chin-Hong said.

You should also wash surfaces with a bleach solution, stay at home if you’re sick and clean fruits, vegetables and shellfish before eating them, he said.

If you are sick with the stomach virus, Chin-Hong said, you shouldn’t prepare food until two days after symptoms are gone.

You should also do laundry and clean your bedding to prevent the virus from spreading.

“Norovirus is very hardy,” he said. “That’s probably the reason why it’s such a threat because it’s harder to kill.”

The state health department said the virus can stay on surfaces for weeks.

According to the CDC, there is no specific medicine to treat norovirus. If you get sick with the stomach flu, the agency advises you to drink plenty of fluids or sports drinks to avoid dehydration. The Mayo Clinic said a doctor may recommend medication for anti-diarrheal medication and nausea.

Typically, illness should resolve within a few days.

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