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.

The CDC said that testing of a person with a severe case of bird flu indicated the virus had mutated but the risk remains low to the public as no human-to-human transmission has been documented.

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.