The Centers for Disease Control and Prevention said Thursday that testing of a person with a severe case of bird flu indicated the virus had mutated when compared with samples taken from infected birds.

The CDC added on Thursday that the virus showed low-frequency mutations in the hemagglutinin gene of a sample sequenced from the patient, suggesting the changes emerged in the patient after infection. The CDC said that the mutations were not found in virus sequences from poultry samples collected on the patient’s property.

The case stems from a Louisiana resident who is believed to have contracted the virus from a backyard flock of poultry. The person was hospitalized and considered to have the first recent severe case of the avian flu in the U.S.

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The CDC said that there is currently no known transmission of the virus from the patient in Louisiana to others. There have been no recorded instances in the U.S. of person-to-person transmission of the virus.

The CDC has noted 65 U.S. cases of the bird flu to date.

Most of these cases have resulted in mild symptoms for patients and a full recovery. However, past cases of bird flu in humans in other countries have been severe, with some resulting in death, according to federal health officials.

Despite the recent sampling, the CDC continues to believe that the risk is low to the public, but cautioned, "The detection of a severe human case with genetic changes in a clinical specimen underscores the importance of ongoing genomic surveillance in people and animals, containment of avian influenza A(H5) outbreaks in dairy cattle and poultry, and prevention measures among people with exposure to infected animals or environments."

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Among the prevention measures are avoiding contact with sick or dead animals, in particular wild birds, and poultry.