H5N1 bird flu infects five more humans in California, and one in Oregon

• Five new human cases of H5N1 bird flu have been detected in California.
• Oregon’s first known human case has been confirmed.
• Authorities say all cases were transmitted from animals to humans; there is no evidence of human-to-human transmission.
• About 75% of wastewater sites monitored in California show evidence of H5.

As H5N1 bird flu spreads among California dairy herds and southward-migrating birds, health officials announced Friday that six more human cases of infection: five in California and one in Oregon — the state’s first.

A seventh presumptive California case is awaiting confirmation from the U.S. Centers for Disease Control and Prevention.

All of the reported cases have been described as mild, and each person is believed to have contracted the illness from infected livestock or poultry. In California, the infections occurred among dairy workers. In Oregon, the patient was a poultry worker.

California’s state epidemiologist, Erica Pan, said that while the announcement of five cases today may sound like a sudden explosion or acceleration in cases, it was an artifact of state reporting deadlines. Three cases had been confirmed by the CDC on Wednesday after California’s reporting deadline. The other two were confirmed Thursday — a day that California does not make reports on case counts.

And there was also a holiday on Monday, which further slowed reporting.

“I would still call these sporadic animals or human infections, and there’s still no evidence of any human to human,” transmission, she said. “These are all workers who are at risk of exposure based on their their work exposures.”

In the Oregon case, the person contracted the disease from a previously reported infected commercial poultry operation outbreak in Clackamas County. A statement from the Oregon Health Authority said there is “no evidence of person-to-person transmission and the risk to the public is low.”

The agency said the person is fully recovered and was treated with oseltamivir, an antiviral medication. The health agency also prescribed the antiviral medication to people who lived in the same home as the patient.

Since March, the U.S. Centers for Disease Control and Prevention has said that 52 people have been infected by the H5N1 virus. Dairy cattle were the source for 30 of those cases, poultry for 21. The source of one more case in Missouri remains unknown.

In addition, a teenager in British Columbia was infected by an unknown source and as of Friday was hospitalized in critical condition.

Twenty-six cases have been identified in California, including the five most recent. All had been in contact with infected dairy cows.

WastewaterScan — an infectious disease monitoring network led by researchers from Stanford University and Emory University, with laboratory support from Verily, Alphabet Inc.’s life sciences organization — follows 28 wastewater sites in California. All but seven have detectable amounts of H5. It is unclear what the source is in each system, but experts say it could be from unpasteurized milk, wild bird droppings or discarded contaminated animal products.

Cities and municipalities that have detected the virus since the beginning of November are: Gilroy, Indio, Lompoc, Los Angeles County, Los Angeles, Marina, Merced, Napa, San Francisco, Ontario, Palo Alto, Redwood City, Riverside, Sacramento, San Diego, San José, Santa Cruz, Southeast San Francisco, Sunnyvale, Turlock and Vallejo.