Signs of avian flu found in San Francisco wastewater

SAN FRANCISCO, CA - MARCH 13: The skyline of downtown San Francisco with the Golden Gate bridge in the foreground taken from Golden Gate view point on Saturday, March 13, 2021 in San Francisco, CA. On March 2, 2021, the San Francisco Department of Public Health updated a COVID-19 health order to allow many businesses to reopen at the Red Tier. (Gary Coronado / Los Angeles Times)
Signs of bird flu have been detected in San Francisco wastewater, although officials are unclear on their origin. Here, the skyline of downtown San Francisco can be seen through the suspension rigging of the Golden Gate Bridge in 2021. (Gary Coronado/Los Angeles Times)

Signs of H5N1 bird flu virus have been detected at three wastewater sites in the San Francisco Bay Area, according to sampling data.

Although 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.

A statement from the state's department of public health noted that its staffers are working with the CDC and local health departments to determine the source of H5 in wastewater. It noted that they are looking at non-human sources, including domestic poultry and wild birds.

"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," department officials wrote 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."

Read more: Is bird flu in cattle here to stay?

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 "There are not many dairy or animal farms in San Francisco."

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

Julie Weiss, Palo Alto’s watershed protection program manager, said her department’s role in the wastewater research “does not extend beyond providing wastewater samples to the research team.” Kate Gibbs, the spokeswoman for Richmond’s West County Wastewater facility, referred all questions to the state.

Although the samples from the Bay Area wastewater sites tested positive for H5, the testing was not specific to H5N1.

However, researchers say a positive genetic identification for H5 is suggestive of bird flu — whether H5N1, the virus that has been found in U.S. dairy cattle (and which has infected three dairy workers ) or H5N2, the subtype implicated in the death of a man in Mexico City earlier this year.

Most human influenza A viruses are of the H1 and H3 variety.

Read more: What you need to know about the bird flu outbreak, concerns about raw milk, and more

The virus has been detected in 133 dairy herds across 12 states. It has also been found in wild birds and domestic poultry flocks throughout the United States.

In recent weeks, H5 was also detected in wastewater samples in Idaho, among other states.

Although there is "no threat to the general public from the H5 detection in wastewater" at this time, said Christine Hahn, Idaho state epidemiologist, "we have determined that it is important that we work to understand these recent findings as much as possible."

The state is workingwith the Centers for Disease Control and Prevention to investigate the issue.

WastewaterSCAN, the research organization that detected the virus, is an infectious disease monitoring network run by researchers at Stanford, Emory University and Verily, Alphabet Inc.’s life sciences organization.

A review of their data — which takes samples from 194 locations across the country — suggests H5 has also been detected at sites in Michigan, Texas, Minnesota, South Dakota and Iowa.

California is the only one of these states that has not reported H5N1-infected cattle.

This story originally appeared in Los Angeles Times.