Bird flu is a disease caused by avian influenza A viruses, according to the CDC. The virus mostly spreads between birds and dairy cows, but there have been 67 human cases of bird flu nationwide and one death tied to the infection since 2024, CDC records show.

The CDC has confirmed a positive bird flu case in a child in San Francisco, the second juvenile case of H5N1 in the country.

A new strain of bird flu has been confirmed at a duck farm in California, the first time the variant has been discovered in poultry in the United States, an