A patient in Missouri who was hospitalized after an infection with bird flu had the H5N1 strain of the virus, the US Centers for Disease Control and Prevention confirmed Friday.

Federal officials are still trying to determine how a Missouri resident with no known exposure to bird flu, contracted the virus.

The Centers for Disease Control and Prevention said Thursday it has yet to identify “a clear source” of infection in a Missouri patient who tested positive for the bird flu virus despite no known contact with poultry or dairy cows.

WASHINGTON — Public health officials are still trying to determine how a Missouri resident contracted bird flu without having any contact with infected animals, but said Thursday there is no evidence of human-to-human transmission taking place in small enclaves or in a more widespread manner.

As bird flu continues to spread through dairy cow herds and poultry flocks, the Missouri case has raised the possibility of human-to-human transmission of bird flu. But officials stressed Thursday there is no evidence of other people being infected and the risk to the general public remains low.

A close contact of a Missouri resident identified as having a human case of the H5N1 avian flu also became sick around the same time, the Centers for Disease Control and Prevention has revealed.

In a disclosure that can't eliminate the possibility that bird flu may have spread from one human to another for the first time, U.S. health officials have reported that a person who lived with a Missouri resident infected with H5N1 became sick the same day.