According to sampling data, signs of the H5N1 bird flu virus have been detected at three wastewater sites in the California Bay Area.
While positive wastewater 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 herd of dairy cows.
Genetic evidence of avian influenza was detected in San Francisco wastewater on June 18 and 26. Additional “hits” of H5 were observed at a site in Palo Alto on June 19, and another on June 10 at 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 recent detections of H5N1 fragments in San Francisco wastewater.”
“As with previous detections reported before mid-May 2024, the source of H5N1 is unclear and an investigation is ongoing,” department officials wrote in a statement. “It may have originated from bird or other animal droppings 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 birds and domestic poultry in the state.
The finding is “worrisome” because of its urban origin, said Devabhaktuni Srikrishna, an entrepreneur who is developing disease detection techniques and the chief executive and founder of PatientKnowHow.com. “There aren't a lot of dairy farms or animal farms in San Francisco.”
There are also no dairy farms in Palo Alto or Richmond.
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 is indicative of 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 implicated in the death of a Mexico City man 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 flocks of domestic birds 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, an Idaho state epidemiologist, “we have determined that it is important that we work to understand these recent findings both 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 any cattle infected with H5N1.
