A Louisiana resident has died after being hospitalized with bird flu in December of last year, marking the first known U.S. death from the virus.

The patient who, “was over the age of 65 and was reported to have underlying medical conditions,” state health officials announced in a statement, tested positive for the virus and developed severe illness after exposure to wild birds and a personal backyard poultry flock that was infested with H5N1.

No other human cases have been identified in the state.

“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,” the U.S. Centers for Disease Control and Prevention (CDC) said in a statement.

The case involved the D1.1 strain of H5N1, the same subtype that caused the severe condition of a 13-year-old girl in Canada late last year.

Genetic sequencing of the Louisiana patient’s virus revealed rare mutations that likely developed during the course of infection, a news release shows.

However, the changes were not found in the animals believed to have transmitted the virus.

“Although concerning, and a reminder that A(H5N1) viruses can develop changes during the clinical course of a human infection, these changes would be more concerning if found in animal hosts or in early stages of infection,” the CDC noted late last year.

Most other bird-to-human cases have occurred in workers at major poultry farms; “this is the first case of H5N1 bird flu in the U.S. that has been linked to exposure to a backyard flock,” the CDC previously said.

The agency also stressed that an eventual case of severe H5N1 avian flu in an American was “not unexpected.”

“Avian influenza A(H5N1) virus infection has previously been associated with severe human illness in other countries during 2024 and prior years, including illness resulting in death,” the CDC stated.

The case does serve as a reminder, however, that anyone with close exposure to birds needs to be careful. “This means that backyard flock owners, hunters and other bird enthusiasts should also take precautions,” the agency said.

At least 66 human bird flu cases have been diagnosed in the United States this year. The majority of the cases have been in California and Washington, and the infections have mostly surfaced in workers who had been in contact with infected poultry or dairy cows.

For now, there’s no evidence that the bird flu is spreading from person to person, and most cases have largely been mild, the main symptom being conjunctivitis, or pinkeye. No cases, or deaths from person to person spread, have been reported.

In Dec. 2024, U.S. health officials reported that the strain of bird flu detected in a California child is similar to the strain spreading through livestock, though the patient had no known exposure to infected animals.

While the findings were not definitive, tests “showed that the virus was very similar to viruses detected in both dairy cattle and poultry as well as to A[H5N1] viruses from previous human infections in dairy workers in California,” the health update from the U.S. Centers for Disease Control and Prevention said.

“This case does not change CDC’s assessment of the immediate risk to the general public, which remains low at this time,” the agency previously stated.

Meanwhile, California health officials also reported last month that their investigation into how the child may have been exposed to bird flu is continuing. The child received flu antivirals and has since recovered.

Richard Webby, a virologist at St. Jude Children’s Research Hospital who studies influenza, said it is unlikely that community spread explains the California case. Instead, other animals that could have come into contact with the virus, such as cats, dogs or rodents, might be contributing to its spread.

In the California case, no person-to-person spread of the virus has been detected and the child’s family members all tested negative.

Bird flu has been spreading in poultry since 2022, and cases in dairy cows began to crop up in March. The virus was discovered in a pig for the first time earlier this year.

Bird flu infections in people — nearly all among farmworkers — have now been confirmed in 10 states.

California accounts for the largest share of human bird flu cases in the country, with 37 confirmed infections. Washington has recorded 11 cases, and Colorado 10, CDC data shows.

In the United States, more than 915 dairy herds in 16 states have been infected since the outbreak in dairy cows was first confirmed last spring. Avian influenza has been spreading in wild and domestic birds in the United States for several years.

“We should be very concerned at this point,” Dr. James Lawler, co-director of the University of Nebraska’s Global Center for Health Security, told the New York Times. “Nobody should be hitting the panic button yet, but we should really be devoting a lot of resources into figuring out what’s going on.”

More information

The CDC has more on bird flu.

SOURCES: U.S. Centers for Disease Control and Prevention, health update, Jan. 6, 2025; CBS News; U.S. Centers for Disease Control and Prevention, health update, Dec. 18, 2024; Louisiana Department of Health, news release, Dec. 13, 2024; U.S. Centers for Disease Control and Prevention, health update, Dec. 10, 2024; California Department of Public Health, news release, Nov. 19, 2024; British Columbia Ministry of Health, news release, Nov. 9, 2024; New York Times

Source: HealthDay