Washington state officials quarantined the Yakima County dairy herd linked to the nation's third human bird flu death on Thursday. They also began testing farmworkers and household contacts of the victim for H5N1 infection. The Washington State Department of Agriculture said no milk or cattle could leave the premises until repeated testing came back negative.

The Yakima County resident, who had underlying health conditions, died after exposure to dairy cows, according to the Washington State Department of Health. The death follows a fatal case in Louisiana in January 2025, the first US H5N1 death, and an H5N5 case in an older resident of Grays Harbor County, Washington, reported in November 2025. Federal health authorities have logged about 70 human H5N1 infections since the virus was detected in American dairy cattle in 2024.

The Centers for Disease Control and Prevention said preliminary genetic sequencing of the patient's sample found no markers associated with efficient transmission between humans. A CDC spokesperson said the agency continued to assess the immediate risk to the general public as low. Full sequencing results, including whether the virus matched strains circulating in Washington cattle, were expected within days.

Yakima County health officials said close contacts had been offered the antiviral oseltamivir as a precaution. The state health department urged dairy workers to wear eye protection and gloves and to report conjunctivitis or flu-like symptoms promptly. Farmworker advocacy groups in central Washington have long warned that many workers lack sick pay and fear losing wages if they come forward.

The case is likely to intensify pressure on the US Department of Agriculture over its national milk testing programme, which began in late 2024. Yakima County is among Washington's largest dairy-producing areas. The state agriculture department said neighbouring herds would be sampled over the coming week.