The Brief

If you feel like you’re seeing more people with stomach issues recently, you may be right. We’re in the midst of peak norovirus season.

Norovirus, nicknamed the stomach flu, is a highly contagious illness that can cause you to experience a host of unpleasant symptoms, like vomiting, diarrhea, and stomach cramps.

Here’s what you should know about how the virus is affecting Southern California.

What’s the spread like?

California’s stomach flu season goes from November to April, according to the state health department. Norovirus has also received attention recently after the FDA issued multiple oyster recalls, and an outbreak occurred at a Pasadena wildfire evacuation center.

Dr. Elizabeth Hudson,  regional chief of infectious diseases for Kaiser Permanente Southern California, said the illness spreads well in very tight areas.

“ It’s pretty much one of the leading causes of any kind of [gastrointestinal] illness in the U.S., and has been for many, many years,” she said.

Exactly how much norovirus is spreading in California can be tough to gauge. Health departments only track reported outbreaks, which the CDC defines as two or more similar illnesses resulting from a common exposure.

For example, the California Department of Public Health recorded 55 laboratory-confirmed outbreaks from January to November last year, which was fewer than the same time period in 2023.

Matt Conens, a department spokesperson, said the numbers don’t reflect the overall community burden of norovirus because most cases are never tested.

With the ones that are, Hudson said she’s seen positivity percentages go up over the last several months — at times ranging from 10% to 25%.

“A lot of people don't necessarily seek care. They kind of say, ‘I’ll take care of myself at home,’” she said. “So I'm sure that’s probably a very large underestimation.”

Recent wastewater monitoring shows significant norovirus activity locally, which can be a more reliable way to determine spread. The city of L.A.’s Hyperion Water Reclamation plant reports "high" amounts of the virus, while the county’s A.K. Warren Water Resource Facility sits at a "medium" rating.

A map that shows wastewater plants and their detected norovirus amount. The shading indicates plant's coverage area, not what specific areas may have norovirus.

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Courtesy WastewaterSCAN

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What to look out for and do

You’re most infectious to others while you’re sick. The 48 hours afterward is also when you shed the most virus, Hudson said.

The virus lives in infected vomit and stool, so it can spread in multiple ways, such as sharing bathrooms, eating contaminated foods, and even touching unclean surfaces that were exposed to the virus weeks ago.

That’s why it’s important to consider isolating if you can, and have those who are caring for you wear masks and use gloves to clean up. That should happen frequently with soap and water, followed by a disinfectant wipe. (Fun fact: Alcohol-based disinfectants, including hand sanitizers, don’t work on norovirus.)

Aside from the possibility of fever and body aches, norovirus can ravage your gastrointestinal tract so much that it makes it hard to keep food or liquids down. The dehydration risk is where much of the concern lies, Hudson said.

“ You can become extremely dehydrated from it,” she said. “You may not be peeing as much. You may also notice when you go to stand up, you start to feel super, super dizzy.”

These are signs that medical help may be needed, especially if the sick person is a child under 5 or an adult over 65. However, most people will be able to get through the illness at home.

Hudson recommends using oral rehydration salts to help.