CHICAGO - The CDC is deploying a team to Washington state to assess the health of farm workers who culled poultry suffering from bird flu after four workers are presumed to have been infected by the virus, US and state health officials said on Monday.

The infections would make Washington the sixth state to identify human cases this year.

The cases fuel growing concern among public health experts, as infections of US dairy cattle and more than two dozen farm workers have worried scientists and federal officials about the risks to humans.

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California and Washington have said they are seeking to administer seasonal flu vaccines to farm workers to reduce their risk of being infected with both bird flu and seasonal influenza.

Infections with both types of virus simultaneously could increase the risk of changes that could make bird flu spread more easily in people and potentially cause a pandemic, virologists say.

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"We don't have evidence yet of transmission between people," said Roberto Bonaccorso, spokesperson for the Washington State Department of Health.

The Centers for Disease Control and Prevention is awaiting specimens for testing from Washington and sending a team to support the state's assessment of farm workers, an agency spokesperson said. The risk to the public from the outbreak in cattle remains low, but those with exposure to infected animals are at heightened risk, according to the CDC.

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The four tested presumptively positive after working at an infected egg farm, Washington's health department said, adding their use of protective gear was inconsistent. The workers suffered mild respiratory symptoms and conjunctivitis, and were given antiviral medication, officials said.

The workers were removing carcasses and litter and cleaning facilities where about 800,000 chickens were culled, the health department said. The farm was hit by a strain of the virus from wild birds, according to Washington's agriculture department.

Nationwide, 27 people had tested positive for the virus in 2024 before the cases in Washington. All but one had known exposure to infected poultry or dairy cattle.

More than 100 million US chickens, turkeys and other birds have been eliminated by the virus since the nation's outbreak began in 2022.