Health officials say the 65-year-old was hospitalized after coming into contact with an infected flock of backyard birds.

A 65-year-old in the southern state of Louisiana was hospitalized in critical condition due to bird flu. This is the first serious case reported in the United States.

The Centers for Disease Control and Prevention (CDC) announced Wednesday that the person had been in contact with an infected flock of backyard birds. No cases of human-to-human transmission have been reported.

“CDC confirms the first serious case of H5N1 bird flu in the United States. “While an investigation into the source of infection is ongoing, it was determined that the patient had contact with sick and dead birds in backyard flocks,” the agency said.

“This case does not change CDC’s overall assessment of the immediate public health risk of H5N1 avian influenza, which remains low.”

Demetre Daskalakis, director of the CDC’s National Center for Immunization and Respiratory Diseases, also told reporters that the Louisiana case was the first to be linked to a non-commercial herd.

While experts emphasize that the threat to public safety is currently low, the spread of the virus has raised questions about how the outbreak is being tested and tracked.

As of Wednesday, the CDC has counted 61 confirmed human cases of bird flu in the U.S., with most of them linked to contact with sick poultry or dairy cows.

Avian influenza, or H1N1, is endemic or occurs regularly in wild bird populations. But its presence in livestock and pets has increased the likelihood of infection in humans.

The CDC said a strain of bird flu was first detected in dairy cows in the United States on March 25. “This is the first time these bird flu viruses have been found in cows,” it said.

Shortly thereafter, on April 1, Texas reported the first human transmission through contact with a dairy cow. Since then, 37 of the 61 human bird flu infections have been linked to infected dairy herds, with California counting 33 cases.

According to the United States Department of Agriculture (USDA), there are 865 infected herds in 16 states. On Wednesday, California declared a state of emergency to contain the outbreak.

“This proclamation is a targeted measure to ensure government agencies have the resources and flexibility they need to respond quickly to this outbreak,” Gov. Gavin Newsom said in a statement.

His statement emphasized that California has “the largest testing and surveillance system in the country to respond to the outbreak.”

“While the risk to the public remains low, we will continue to take all necessary steps to prevent the spread of this virus,” Newsom said.

Some farmers have resisted the push to test livestock for bird flu, and the U.S. government itself has largely resisted mandating mandatory testing, instead relying on voluntary efforts.

But that stance changed on Dec. 6, when the U.S. Department of Agriculture’s Animal and Plant Health Inspection Service announced it would test samples of raw, unpasteurized milk from herds nationwide.

The federal regulation requires all dairy farms, milk transporters and milk processing plants to pass on raw milk samples upon request.

Herd owners are also required to share any information about the spread of disease among their cattle so that federal authorities can track the spread of bird flu.

However, the B3.13 genotype associated with avian influenza in cattle is different from the strain in the Louisiana case, known as the D1.1 genotype. The CDC confirmed this case on Friday but did not release its results until Wednesday.

In two cases — one in a child in California and one in an adult in Missouri — the CDC has not yet determined how the patients became infected. A Canadian teenager was also hospitalized last month with a severe case of bird flu.

Since the outbreak began in the United States in 2022, bird flu has killed 123 million poultry.