State health officials said Sunday that bird flu virus was detected in a retail sample of raw milk from Fresno-based dairy Raw Farm.

The sample was collected by officials with the Santa Clara County public health office, who have been testing raw milk products from retail stores “as a second line of consumer protection.”

County officials identified the virus in “one sample of raw milk purchased at a retail outlet” on Nov. 21, according to statements from both the state and the county. The county contacted stores on Friday and recommended they pull the raw milk from sale. The test results were confirmed on Saturday by the California Animal Health and Food Safety Laboratory System at UC Davis.

“This isn’t surprising, given how quickly H5N1 seems to be spreading among farms in California and given the fact that these outbreaks on farms are being discovered in large part due to bulk testing of raw milk from farms,” said Jennifer Nuzzo, director of the Pandemic Center at Brown University in Providence, R.I. “What we don’t know is how much risk H5N1 poses to people that drink unpasteurized, infected milk.”

The test was positive only for the “H5” part of the virus. However, health officials say an H5 finding in a California dairy product is likely H5N1. No other H5 bird flu viruses have been detected in dairy cows.

Raw Farm has issued a voluntary recall for all quart- and half-gallon-sized milk products produced on Nov. 9, with an expiration date of Nov. 27, with a lot ID of #20241109.

So far, there have been no reports of illness associated with this recall.

“Out of an abundance of caution, and due to the ongoing spread of bird flu in dairy cows, poultry, and sporadic human cases, consumers should not consume any of the affected raw milk,” state health officials wrote in a statement.

Nuzzo said evidence from animal studies suggests the virus “could pose a risk if ingested in large enough quantities, but we have not yet seen human cases resulting from raw milk consumption. Given that ingestion of raw milk has no credible health benefits, I personally would avoid drinking it.”

Researchers have found that barn cats that drink raw milk tend to die as a result of their exposure. And laboratory studies have shown similar results.

Last week, the CDC reported samples taken from a child in Alameda County who was showing mild respiratory symptoms were positive for H5N1. It is unclear how the child was exposed to the virus, although investigators ruled out exposure to infected dairy or poultry animals. They also ruled out raw milk.

Throughout California, 29 people have tested positive for the virus, and all but one — the child in Alameda County — are dairy workers. Nationwide, the number is 55, with 32 exposed via dairy, 21 via poultry, and two with no known source.

In addition, a teenager in British Columbia was also infected, and has remained in critical condition for more than two weeks. The source of that child’s infection also remains unknown.

There is no evidence of person-to-person transmission of the virus.

Since March, 402 California dairy herds have tested positive in the state; 616 herds have tested positive nationwide.

Mark McAfee, the owner of Raw Farm, said that the testing he and the California Department of Food and Agriculture have conducted on his milk — since he started voluntary testing in late April — has all been negative.

“In the last two days CDFA has collected extra dairy samples from our farm bulk tanks and even retail samples and they are all officially Negative for HPAI,” he wrote in a statement. HPAI is the acronym for highly pathogenic avian influenza; it is often used interchangeably with H5N1, as well as other highly pathogenic bird influenza strains.

The California Department of Public Health confirmed that the agriculture department had tested McAfee’s milk after receiving news of the finding, and results were negative.

Raw Farm is the largest producer and retailer of raw milk in the state, where the product is legally sold in retail stores. McAfee said he has about 1,800 head of cattle on two dairies — one in Fresno, the other near Hanford.

The U.S. Food and Drug Administration does not allow for the interstate transfer of raw milk for human consumption, and advises the public not to drink or consume raw milk products. Officials say that pasteurization inactivates the virus.

Several states have recently changed laws to legalize raw milk products, including Iowa, Louisiana and Delaware — which all changed laws this spring allowing for wider consumer access.

In addition, President-elect Donald Trump’s nomination for Health and Human Services, Robert F. Kennedy, Jr., is a vocal proponent of raw milk and has said he wants to increase people’s access to unpasteurized milk.

The Raw Farm recall notice requests that stores remove the product from shelves and urges consumers to return the product to the store from which it was purchased for a free replacement or refund.

McAfee said it is unlikely any of the product remains on store shelves.

“It’s all gone,” he said. “We take back anything that doesn’t sell after seven days.”

The virus has shown up in wastewater sites across Santa Clara County, including Palo Alto, San Jose, Gilroy and Sunnyvale.

It’s also been detected in 24 of the 28 California wastewater systems tested by WastewaterScan — an infectious disease monitoring network led by researchers at Stanford and Emory University, with lab testing partner Verily, Alphabet Inc.’s life sciences organization.

We are living in a “very highly charged time for raw milk,” McAfee said. “It’s all over the news with RFK announcing he wants raw milk for everyone to improve the immunity and gut microbiome for America.”

“Our mission is to nourish our consumers with the highest quality raw milk and that is what we are doing,” he said, citing his testing protocol and history with the state’s agriculture department.