As H5N1 bird flu spreads among California dairy herds and migratory birds southward, health officials on Friday announced six more human cases of infection: five in California and one in Oregon, the first in the state .
A seventh presumptive case from California is awaiting confirmation from the US Centers for Disease Control and Prevention.
All reported cases have been described as mild and each person is believed to have contracted the disease from infected livestock or poultry. In California, infections occurred among dairy workers. In Oregon, the patient was a poultry worker.
California State Epidemiologist Erica Pan said that while the announcement of five cases today may seem like a sudden explosion or acceleration of cases, it was an artifact of state reporting deadlines. The CDC confirmed three cases Wednesday after California's reporting deadline. The other two were confirmed Thursday, a day when California does not report case counts.
And there was also a holiday on Monday, which further slowed down reporting.
“I would still call these sporadic infections animal or human, and there is still no evidence of human-to-human transmission,” he said. “These are all workers who are at risk of exposure because of their occupational exposure.”
In the Oregon case, the person contracted the disease from a previously reported outbreak of an infected commercial poultry operation in Clackamas County. A statement from the Oregon Health Authority said “there is no evidence of human-to-human transmission and the risk to the public is low.”
The agency said the person has fully recovered and was treated with oseltamivir, an antiviral medication. The health agency also prescribed the antiviral drug to people who lived in the same house as the patient.
Since March, the US Centers for Disease Control and Prevention has said 52 people have been infected by the H5N1 virus. Dairy cattle were the source of 30 of those cases and poultry were the source of 21. The source of one additional case in Missouri is unknown.
Additionally, a teenager in British Columbia was infected from an unknown source and was hospitalized in critical condition as of Friday.
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 at Stanford University and Emory University, with lab support from Verily, Alphabet Inc.'s life sciences organization, follows 28 wastewater sites in California. All but seven have detectable amounts of H5. It's unclear what the source is in each system, but experts say it could be unpasteurized milk, wild bird droppings or discarded contaminated animal products.
Cities and municipalities that have detected the virus since early 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 Jose, Santa Cruz, Southeast San Francisco, Sunnyvale, Turlock and Vallejo.
