Wash those hands extra well, as portions of the Bay Area are experiencing spikes in norovirus infections, the highly contagious gastrointestinal bug that’s typically foodborne, including parts of San Francisco, Marin County, and Silicon Valley.

As SFGate reports, based on data from WastewaterSCAN, higher levels of norovirus infections were detected in the wastewater of the western side of San Francisco, as well as Central Marin County, Novato, and Redwood City. Based on the site’s line graph data, moderate levels were found on the eastern side of SF, Santa Rosa, Vallejo, San Jose, and Palo Alto.

Common norovirus symptoms include vomiting, diarrhea, and stomach cramps, along with fever, headache, and body aches, which typically develop 12 to 48 hours after exposure, according to the US Centers for Disease Control. The virus can lead to dehydration, especially in small children and elderly adults, and it’s advised to drink plenty of fluids, including electrolyte beverages and oral rehydration drinks depending on the severity.

The virus, which is highly contagious, is typically spread through contaminated surfaces and food, as well as coming into contact with those with the virus. The CDC also warns that raw shellfish, including oysters, can also carry the norovirus.

“It is extremely contagious,” Dr. Monica Gandhi, an infectious disease specialist at UC San Francisco, told SFGate, emphasizing that hand-washing is essential. “And people don’t wash their hands, especially kids.”

Per SFGate, the norovirus is often referred to as the “cruise ship bug.” As CBS News reports, more than 150 people became infected onboard a Princess cruise ship last week — out of about 7,000 passengers and crew members, originating in Fort Lauderdale, Florida and sailing through the Caribbean.

In February, there was an outbreak of an "unknown gastrointestinal illness" infecting 27 people aboard the luxury cruise ship, the Regent Seven Seas, which sailed from Miami to Honolulu. Last December, more than 80 people contracted the norovirus on board a Holland America cruise ship, also originating in Fort Lauderdale, as CBS reports.

The site Global Biodefense reports that in 2024, 16 cruise ships encountered outbreaks of gastrointestinal disease, including five in December 2024 alone — reportedly the largest number of outbreaks in 12 years.

Image: The US Centers for Disease Control

Many Americans have had an unpleasant surprise during these past couple celebration-filled weeks, and that surprise was a gastrointestinal virus.

Norovirus makes its rounds on cruise ships on the regular, and tends to rear its ugly head around the holiday season. But this year appears to be somewhat special, as the Centers for Disease Control is reporting an uptick in norovirus outbreaks and a surge in general being seen across the country.

Headlines in recent weeks in Bay Area focused on oyster-borne norovirus cases, with some cases having been linked to raw oysters coming from British Columbia, which have since been recalled.

But there have been other outbreaks not linked to shellfish, like one in early November in Santa Cruz County that shut down an elementary school in Aptos. And as the Associated Press reports via the CDC, there were 91 separate norovirus outbreaks recorded across the country during the week of December 5, an uptick from 69 outbreaks in the last week of November.

This also marks a surge compared to recent previous years, when the CDC recorded a maximum of 65 outbreaks in that first week of December.

CBS News Minnesota also reported an unusual high number of cases in December as well — and these reports likely reflect only a fraction of the number of cases, given that individuals' symptoms typically pass within about 24 hours and they may never go to a doctor.

Dr. Leana Wen, a former health commissioner in Baltimore, spoke about the CDC data and the norovorus outbreak on Face the Nation on Sunday.

"Norovirus is the most common foodborne illness here in the U.S. It's very hard to avoid once it's in your family," Dr. Wen said. "And, also, don't prepare food if you're having vomiting, diarrhea, stomach cramps, because you don't want to spread it to other people."

Norovirus is term that refers to a group of similar viruses that spread easily and cause vomiting, diarrhea, stomach cramps, fever, and dehydration. While symptoms typically pass in one to three days, small children and older adults, especially those with weakened immune systems, can suffer complications and more serious cases.  Out of 19 to 21 million estimated annual cases of norovirus in the country, an average of 900 people die each year from the infection.

The best defense against norovirus is rigorous scrubbing of hands before eating or touching one's face, and preventing people who are infected from preparing food, which can be another source of infection. The virus also tends to spread in confined spaces like cruise ships, airplanes, and college dorms.

Top image: Photo by Smith Collection/Gado/Getty Images

At the risk of sounding like an alarmist, SFist received word today about a possible virus outbreak in San Francisco. It's the Norovirus, a common cause of the stomach flu, which is "transmitted by faecally contaminated food or water [Ew! -- SFist] and by person-to-person contact."

Thankfully, the JavaOne conference team at Moscone Center was notified before any citizens. Check it:

The JavaOne conference team has been notified by the San Francisco Department of Public Health about an identified outbreak of a virus in the San Francisco area. Testing is still underway to identify the specific virus in question, but they believe it to be the Norovirus, a common cause of the "stomach flu", which can cause temporary flu-like symptoms for up to 48 hours. Part of the San Francisco area impacted includes the Moscone Center, the site of the JavaOne conference which is being held this week. We are working with the appropriate San Francisco Department of Public Health and Moscone representatives to mitigate the impact this will have on the conference and steps are being taken overnight to disinfect the facility. We have not received any indication that the show should end early, so will have the full schedule of events on Friday as planned. We hope to see you then.

For further information, as well as Frequently Asked Questions related to the Norovirus, please visit the San Francisco Department of Public Health website at http://sfcdcp.org/norovirus.cfm

Update: The Gate has more on the Moscone Center bug, which has led to violent diarrhea and vomiting. [insert your own joke here]

Micrograph of the noroviruses: Wikicommons