Signs of the H5N1 avian influenza virus have been detected at three wastewater sites in California’s Bay Area, according to sampling data.
While positive sewage samples have been found in seven other states, California is the only one that has yet to report an outbreak of bird flu in a dairy herd.
Genetic evidence of bird flu was detected in San Francisco wastewater on June 18 and 26. Additional H5 “results” were detected at a site in Palo Alto on June 19 and another on June 10 at the West County wastewater plant 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 recent detections of H5N1 fragments in San Francisco wastewater.”
“As with previous detections reported before mid-May 2024, the source of the H5N1 is unclear and an investigation is ongoing,” department officials wrote in a statement. “It may have originated from bird or other animal waste due to San Francisco’s sewer system collecting and treating 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 has been found in wild and domestic birds in the state.
The finding “is concerning” because of its urban origin, said Devabhaktuni Srikrishna, an entrepreneur developing disease-detection techniques and CEO and founder of PatientKnowHow.com. “There aren’t many dairy or animal farms in San Francisco.”
There are no dairy farms in Palo Alto or Richmond either.
The manager of the Palo Alto plant was not in the office Friday and was unable to comment. A spokesman for the Richmond plant directed questions to the state.
A request for comment from the state’s Wastewater Monitoring Program has not yet been responded to.
Although samples from Bay Area wastewater sites tested positive for H5, the test was not specific for H5N1.
However, researchers say that a positive genetic ID for H5 suggests bird flu, either H5N1, the virus that has been found in U.S. dairy cattle (and which has infected three dairy workers) or H5N2, the subtype involved in the death of a man. from Mexico City this month.
Most human influenza A viruses are of the H1 and H3 varieties.
The virus has been detected in 133 dairy herds in 12 states. It has also been found in wild birds and domestic poultry throughout the United States.
In recent weeks, H5 has also been detected in wastewater samples in Idaho, among other states.
While “there is no threat to the general public from the detection of H5 in wastewater” at this time, said Christine Hahn, Idaho state epidemiologist, “we have determined that it is important for us to work to understand these recent findings as much as possible.”
The state is working closely with 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 (covering samples from 194 sites across the country) suggests that 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 cattle infected with H5N1.