The US reported its first severe human case of bird flu on Wednesday (Dec 18) in a Louisiana resident who is hospitalised in critical condition after suspected contact with an infected backyard flock.

California, the most populous state, declared an emergency over the H5N1 virus as it spread more widely in dairy herds and after it has infected dozens of farm workers this year.

Federal and state officials have failed to control the nation's outbreak, which infected dairy cattle for the first time in 2024, as some farmers resist testing and containment measures.

Severe respiratory illness in the Louisiana patient shows increased health risks for people from the virus that previously caused eye redness, or conjunctivitis, in infected dairy workers.

Bird flu still represents a low risk to the general public, the US Centres for Disease Control and Prevention said.

CDC has confirmed 61 human cases nationally since April, mostly in workers on dairy farms where the virus infected cattle. Workers culling infected poultry also have tested positive.

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