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 the bird flu in the body of a Louisiana man who contracted the first severe case found it mutated inside of his body, a development that could allow the virus to more easily spread to humans.

A genetic analysis of samples from the patient in Louisiana recently hospitalized with the country’s first severe case of H5N1 bird flu show the virus likely mutated in the patient to potentially become more transmissible to humans,