A genetic analysis suggests the bird flu virus mutated inside a Louisiana patient who contracted the nation’s first severe case of the illness, the U.S. Centers for Disease Control and Prevention said this week.

A genetic analysis of viral samples from a patient in Louisiana hospitalized with the first severe case of bird flu showed mutations that may result in the virus becoming more transmissible

The CDC has confirmed a total of 66 human cases of bird flu across the United States as of Friday, although the number is believed to be higher.