The Louisiana Department of Health said on Monday that a U.S. patient hospitalized with H5N1 bird flu has died, the country's first death from an outbreak of the virus that has sickened dozens of people and millions of poultry and cattle.

Nearly 70 people in the U.S. have contracted bird flu since April, according to the U.S. Centers for Disease Control and Prevention (CDC), most of them livestock workers exposed to sick chickens or dairy cattle.

The patient in Louisiana, the first person in the country to be hospitalized with the virus, contracted bird flu after coming into contact with sick and dead chickens and wild birds in a backyard flock, said Louisiana health officials.

The patient, who state health officials said was over 65 and had underlying medical conditions, was hospitalized on Dec. 18, 2024.

State officials previously said the individual was a resident of southwestern Louisiana. No details were provided about when the death occurred.

There is no sign that the virus is spreading from person to person, a key trait that scientists watch for in assessing the pandemic potential of a flu virus.

In a statement, the CDC confirmed the Louisiana individual was the first person to die as a result of H5 bird flu in the U.S.

"CDC has carefully studied the available information about the person who died in Louisiana and continues to assess that the risk to the general public remains low. Most importantly, no person-to-person transmission spread has been identified."

Mutations similar to those found inside B.C. patient

The U.S. officials also said a genetic analysis had suggested the bird flu virus had mutated while inside the Louisiana patient. The mutations may have increased the virus's capacity to attach to cells in the upper respiratory tract, a technical summary from the CDC suggests.

Samples from a teenager in British Columbia showed similar mutations, Canadian and U.S. researchers reported last week. They said the 13-year-old girl had been in critical care and no longer needs supplemental oxygen.

B.C. teen with severe avian flu now out of ICU, no longer infectious

Both patients carried a version of the virus found in wild birds rather than what's behind the outbreak in U.S. dairy cattle.

Previous illnesses in the U.S. have been mild, and most have been detected among farm workers exposed to sick poultry or dairy cows. In two cases — an adult in Missouri and a child in California — health officials have not determined how they caught it.

"While the current public health risk for the general public remains low, people who work with birds, poultry or cows, or have recreational exposure to them, are at higher risk," the Louisiana department said in a statement.

Most U.S. bird flu cases in humans reported mild symptoms, including conjunctivitis, or pink eye.

Wake-up call for public health?

"Though H5N1 cases in the U.S. have been uniformly mild, the virus does have the capacity to cause severe disease and death in certain cases," said Dr. Amesh Adalja, senior scholar at the Johns Hopkins Center for Health Security in Baltimore. The Louisiana patient was at high risk from influenza given their age and underlying conditions, he said.

The death is not surprising given that bird flu has killed people in other countries, said Gail Hansen, a veterinary and public health consultant.

"I hate to have the death of somebody be a wake-up call," she said. "But if that's what it takes, hopefully, that will make people look at bird flu a little more carefully and say this really is a public health issue we need to be looking at more closely."