Officials are warning the public not to consume raw oysters in at least two California counties after several people became sick with norovirus.

San Diego County health officials have linked 41 confirmed and probable cases of the illness to raw oysters imported from a specific harvest in Northwest Mexico, the county said in a press release Jan. 11.

The cases started to appear in mid-December after people ate the raw shellfish from Sonora, Mexico, according to health officials.

The oysters have only been sold by restaurants and wholesalers. County health officials have asked restaurants to set aside “Rocky Point” oysters packed by GolPac located in Sonora, Mexico, until further notice, according to the press release.

Restaurants that bought oysters from the company are asked not to use them while an investigation continues.

Cases have been tied to oysters served at The Fish Shop restaurants in Pacific Beach, Point Loma, Encinitas, and the Carlsbad Aquafarm. The health agency said other locations might be added during the investigation.

Illness caused by norovirus can include vomiting and diarrhea among people of all ages.

Those who were sickened ranged between 12 to 83 years old and reported eating raw oysters a day or two before symptoms started, the San Diego health agency reported.

Other household members, including children, who did not eat the oysters have also become sick, likely due to spread within the home, according to health officials.

None of the illnesses required hospitalization.

In Los Angeles County, raw oysters were linked to 27 cases of gastrointestinal illness. The county’s public health department is investigating a cluster of illnesses potentially linked to raw oysters eaten at four local restaurants.

Los Angeles County public health officials warned residents Jan. 12 to be vigilant.

“Until the source is confirmed, consumers should be cautious before eating raw oysters due to the potential risk of foodborne illness,” said Muntu Davis, a Los Angeles County health officer. “If you are sick, avoid spreading illness by washing your hands frequently and cleaning frequently touched surfaces, such as doorknobs, light switches, and kitchen countertops.”

The United States Food and Drug Administration (FDA) also warned restaurants and food retailers not to serve or sell oysters from Sociedad Acuicola GolPac harvested from Sonora, Mexico on Dec. 18, 2023, or Dec. 27, 2023, due to norovirus contamination. The agency also asked them to dispose of any of the products by throwing them in the garbage or returning them to their distributor for destruction.

The FDA is waiting for more information about the distribution of the oysters harvested and will continue to monitor the issue and provide help to state authorities, the agency reported.

People who contract norovirus usually develop nausea, vomiting, diarrhea, stomach cramps, fever, and body aches about 12 to 48 hours after eating contaminated foods. The illness usually lasts up to three days.

The vomiting and diarrhea can lead to dehydration, requiring medical attention, especially in young children, older adults, and people with other illnesses.