LOS ANGELES — Signs of H5N1 bird flu virus have been detected at three wastewater sites in California’s Bay Area, according to sampling data.

While positive wastewater samples have been found in seven other states, California is the only one that has yet to report a bird flu outbreak in a herd of dairy cows.

Genetic evidence of bird flu was detected in San Francisco wastewater on June 18 and June 26. Additional H5 “hits” were seen at a site in Palo Alto on June 19, and another on June 10 from the West County Wastewater facility in Richmond.

According to the San Francisco Department of Public Health, officials have been closely monitoring H5N1 along with federal, state and local partners, and are “aware of the recent detections of fragments of H5N1 in San Francisco’s wastewater.”

“As with the previous detections reported from before mid-May 2024, it is unclear what the source of H5N1 is, and an investigation is ongoing,” wrote department officials in a statement. “It is possible that it originated from bird waste or waste from other animals due to San Francisco’s sewer system that collects and treats both wastewater and stormwater in the same network of pipes.”

Health officials said the risk remains low for the general public.

The virus has not been identified in California cows, but it has been found in wild birds and domestic poultry in the state.

The finding “is concerning” because of their urban origin, said Devabhaktuni Srikrishna, an entrepreneur who is developing techniques for disease detection, and the chief executive and founder of PatientKnowHow.com. “There are not many dairy or animal farms in San Francisco.”

There are also no dairy farms in Palo Alto or Richmond.

The plant manager from Palo Alto was out of the office Friday, so could not comment. A spokesperson for the Richmond site directed questions to the state.

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