Bird flu has infected three more people from Washington state after they were exposed to poultry that tested positive for the virus, according to health authorities in Washington and in Oregon, where the human cases were identified.

A total of 39 people have tested positive for bird flu in the U.S. this year, including nine from Washington, as the virus has infected poultry flocks and spread to more than 400 dairy herds, federal data show. All of the cases were farm workers who had known contact with infected animals, except for one person in Missouri.

The people from Washington cleaned facilities at an infected chicken farm after birds were culled to contain the virus, the Washington State Department of Health said in an email on Thursday.

Officials tested workers who had symptoms, including red eyes and respiratory issues, and those with potential exposure to the birds, the department said. People with symptoms were told to isolate and given antiviral treatment, it added.

Oregon identified the three new cases after the people traveled to the state from Washington while infected, the Oregon Health Authority said in a Thursday statement. They have since returned to Washington, where public health staff are monitoring them, according to the statement.

There have been no infections among people living in Oregon and there is no evidence of human-to-human transmission, the Oregon Health Authority said. It said the risk for infection to the general public remains low.

Since 2022, the virus has wiped out more than 100 million poultry birds in the nation's worst-ever bird flu outbreak.

H5N1 bird flu was confirmed in a pig on a backyard farm in Oregon, the first detection of the virus in swine in the country, the U.S. Department of Agriculture said on Wednesday.