H5N9 is a rare subtype of the influenza A virus that can cause highly pathogenic avian influenza (HPAI), also known as bird flu. It's a reassortment strain that originated from the H5N1, H7N9, and H9N2 subtypes.

The United States has reported its first H5N9 bird flu outbreak in California, affecting almost 119,000 ducks. Both H5N9 and the more common H5N1 strains were found. The USDA is conducting investigations and enhanced surveillance,

According to the Centers for Disease Control and Prevention, 67 people in the U.S. have been infected with H5N1 bird flu. One person has died.