Los Angeles County health officials said they detected the H5N1 avian flu virus in wastewater collected from the AK Warren Water Resources Facility in Carson.
The viral “hit” was detected Oct. 28 by WastewaterSCAN, an infectious disease surveillance network run by researchers at Stanford, Emory University and Verily, Alphabet Inc.’s life sciences organization. .
Successes were also seen last week in San Jose, Redwood City, San Francisco, Palo Alto, Sacramento, Santa Cruz, Marina and Turlock.
The Carson plant treats wastewater from about 50% of Los Angeles County’s population, said Annabelle de St. Maurice, director of community outbreaks and syndromic surveillance for the Los Angeles County Department of Public Health .
Officials say they have not identified the source of the virus, but suggest a few possibilities, including discarded contaminated animal products and feces from infected wild birds. They also “actively engage key at-risk groups,” including nearby dairy and meat processing sites.
“The likely sources seem more likely to be from animal products than wild birds,” De St. Maurice said.
She said the risk to the public remained low.
H5N1 avian flu has been detected in 203 California dairy herds since August; 17 dairy workers were also infected. Nationwide, 41 people have been infected – 21 from dairy cows, 19 from poultry and one unknown. The USDA reported 404 positive dairy herds in 14 states. This number does not include eight herds detected earlier this week in Utah.
It was also conclusively detected in an Oregon pig.
De St. Maurice said the county routinely monitors and tests symptomatic birds, pets and wild mammals.
Additionally, she said, the county is working within the community to subtype flu samples collected at health clinics and hospitals “to see if there are potential human cases of H5N1.”
She noted that the county public health department is also conducting “outreach and education to at-risk communities,” but said so far there have been no human cases.
De St. Maurice said it was this kind of work – subtyping flu samples – that allowed Missouri health officials to identify a human case of H5N1 without contact with dairy or poultry. The source of this person’s infection has still not been determined.
The wastewater findings come as the virus spreads among California’s dairy cows — which now account for more than half of the country’s reported bovine infections — and as the fall migration of wild birds from the Arctic shifts to south along the Pacific Flyway.
There are now two strains of H5N1 bird flu circulating in California. The form circulating in dairy cows is known to scientists as B3.13. A new version of wild birds that has appeared recently is known as D1.1 or D1.2.
Genetic sequencing of the H5 virus found in Los Angeles County wastewater has not been done. According to De St. Maurice, the way samples are captured and identified does not allow for sequencing.
H5 viruses are of avian origin; they are not human viruses.
In a statement, officials said people could reduce their risk of infection by avoiding raw milk, raw cheese and undercooked meats. Pasteurization and proper cooking inactivate the virus.
They also recommend people avoid unprotected contact with sick or dead animals, as well as avoid materials contaminated with bird droppings. Pets can also be infected in this way. And officials are asking people to report sick or dead birds to local animal control agencies.
They also recommend that people get the flu vaccine every year. Although seasonal flu vaccination does not prevent infection with bird flu, it reduces the chance of bird flu combining with human flu, potentially creating a new virus that could spread more easily between humans.
