A genetic analysis suggests the bird flu virus mutated inside a Louisiana patient who contracted the first severe case of the illness in the United States. The U.S.

Genetic analysis of H5N1 bird flu viruses from a severely ill patient in Louisiana revealed multiple mutations that may enhance the virus’s ability to bind to human upper airway cells, the Centers for Disease Control and Prevention (CDC) reported on Thursday.

The first severe case of H5N1 bird flu was confirmed in Louisiana. Here is a map of other states that have been affected.