The U.S. Centers for Disease Control and Prevention has found mutations in samples taken from a man infected with the first severe case of avian influenza in the United States, mutations that were not present in specimens collected from his infected backyard flock.

Despite the discovery of the mutations, the CDC said the risk to the general public remains low.

The detection of a severe human case of bird flu with genetic changes in a clinical specimen “underscores the importance of ongoing genomic surveillance in people and animals,” the agency said.