Federal health officials are addressing the first severe case of bird flu detected in a human during the U.S. outbreak.
Louisiana health officials initially reported the infection last week, saying a person was hospitalized after being exposed to sick and dead birds in backyard flocks.
On Wednesday, the Centers for Disease Control and Prevention shared their findings that indicate the H5N1 virus responsible for the illness belongs to a genetic lineage that's circulating in wild birds and poultry -- different from what's spreading in dairy cattle and driving the majority of infections in agricultural workers.
In the U.S., more than 60 people have been infected so far, although some research suggests the official tally may be an undercount.
The illnesses linked to dairy cattle have largely led to mild illnesses in humans.
The version of the virus in the Louisiana case is the so-called "D1.1 genotype." It has previously popped up in poultry workers in Washington state, who developed mild symptoms after testing positive in October. More recently, however, a teenager in British Columbia was hospitalized after contracting this D1.1 strain of the virus.
Canadian health officials were unable to figure out how that person was infected.
The case in southwest Louisiana was detected during routine flu surveillance and eventually sent to the CDC for confirmation. There's no indication the person spread bird flu to others, and the case doesn't change the CDC's assessment that the risk to the general public remains low.
Still, the hospitalization is a reminder that bird flu has a well-established history of leading to severe illness and death over the past 20 years in other countries, Dr. Demetre Daskalakis with the CDC, told reporters on Wednesday during a press call.
Daskalakis said his agency is doing additional sequencing to look for any worrying changes in the virus that could signal it's evolving to better infect humans or cause more severe disease.
Scientists were concerned that the case in British Columbia exhibited certain mutations that could spell trouble, although more research was needed to understand the exact implications.
Daskalakis referred reporters to Louisiana officials conducting the investigation into the case for further details on how the person caught the virus and their symptoms.
As with the Louisiana infection, most cases have been linked back to some kind of exposure to sick animals. Dairy cattle harbor high loads of virus in their milk and that's suspected to be causing infections in farm workers. Those working with infected poultry can also catch the virus.
However, several cases have cropped up in the U.S. that can't be tracked back to infected farm animals, including in California and Missouri.
"Infections without a clear source of exposure do occur, neither these cases nor the cases with known animal or animal products exposure have resulted in human to human transmission," said Daskalakis.