Sampling data shows signs of the H5N1 bird flu virus have been found at three sewage treatment sites in California's Bay Area.
Although positive wastewater samples have been found in seven other states, California is the only state that has not yet reported an outbreak of bird flu among a herd of dairy cows.
On June 18 and 26, genetic evidence of bird flu was detected in San Francisco's wastewater. Additional H5 hits were observed on June 19 at a site in Palo Alto, and again on June 10 from the West County Wastewater facility in Richmond.
According to the San Francisco Department of Public Health, officials along with federal, state and local partners are closely monitoring the H5N1 outbreak and are “aware of recent detections of fragments of H5N1 in San Francisco wastewater.”
“As with previous detections reported prior to mid-May 2024, the source of H5N1 is unclear and an investigation is ongoing,” department officials wrote in a statement. “It is possible that it came from bird droppings or other animal waste, thanks to San Francisco’s sewer system, which collects and treats both wastewater and stormwater in the same network of pipes.”
Health officials said the risk to the general public remains low.
The virus has not been found in cows in California, but it has been found in wild birds and poultry in the state.
The finding is “concerning” because of their urban origins, said Devabhaktuni Srikrishna, an entrepreneur developing techniques for disease detection and the CEO and founder of PatientKnowHow.com. “There aren't many dairy or livestock farms in San Francisco.”
There are also no dairy farms in Palo Alto or Richmond.
The Palo Alto plant manager was out of the office Friday and could not comment. A spokesman for the Richmond site referred questions to the state.
A request for comment from the state's Wastewater Surveillance Program had not yet been returned.
Although samples from Bay Area wastewater sites tested positive for H5, the tests were not specific for H5N1.
However, researchers say a positive genetic identification for H5 is reminiscent of bird flu – whether it is H5N1, the virus found in US 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 variety.
The virus has been found in 133 dairy herds in 12 states. It has also been found in wild birds and poultry flocks in the United States.
In recent weeks, H5 has also been found in wastewater samples in Idaho. among other states.
While there is currently “no danger to the general public from the detection of H5 in wastewater,” said Idaho state epidemiologist Christine Hahn, “we have determined that it is important that we work to best understand these recent findings.”
The state is working with the Centers for Disease Control and Prevention to investigate the problem.
WastewaterSCAN, the research organization that detected the virus, is an infectious disease monitoring network run by researchers from Stanford, Emory University and Verily, the life sciences organization of Alphabet Inc.
An analysis of their data, which came from 194 sites across the country, found that H5 was also found in places in Michigan, Texas, Minnesota, South Dakota and Iowa.
California is the only state that has not reported any H5N1-infected livestock.
