Bird flu: Louisiana patient is first severe case and California declares emergency

Health officials on Wednesday confirmed the first known severe illness in the U.S. caused by bird flu, and California's governor declared a state of emergency as the virus rampages through dairy cattle in that state.

A person in Louisiana is hospitalized in critical condition with severe respiratory symptoms caused by a bird flu infection, state health officials said. The person, who is over 65 and has underlying medical problems, had been in contact with sick and dead birds in a backyard flock.

It's the first human case in the U.S. linked to exposure to backyard birds, according to the Centers for Disease Control and Prevention.

Since March, more than 60 bird flu infections in people have been reported in the U.S., but previous illnesses have been mild and most have been detected among farmworkers exposed to sick poultry or dairy cows. In two cases — and adult in Missouri and a child in California — health officials have not determined how they caught it.