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A patient in Louisiana has been hospitalized with a severe case of H5N1 bird flu, the U.S. Centers for Disease Control and Prevention said, the first such case in the United States.

The agency said Wednesday that the person had been exposed to sick and dead birds in backyard flocks; This is the first case of bird flu in the United States linked to a backyard flock.

“The patient reported by Louisiana is believed to have had contact with sick or dead birds on his property. “This is not commercial poultry and there has been no exposure to dairy cows or related products,” said Dr. Demetre Daskalakis, director of the National Center for Immunization and Respiratory Diseases at the CDC.

Federal officials declined to answer questions about the patient’s symptoms or his current condition. Instead, they referred all inquiries about the case to the Louisiana Department of Health, which is leading the investigation.

This virus, D1.1, is the same type that recently appeared in humans in Canada and Washington state and has been detected in wild birds and poultry in the United States. It is different from B3.13, the type found in dairy cows, some poultry outbreaks and other human cases in the United States.

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The CDC said it is working on additional genomic sequencing of samples from the patient, who is from southwest Louisiana, and the investigation into the patient’s exposure is ongoing.

In other countries, bird flu has been linked to serious human illness and death. No person-to-person transmission has been detected. “This case does not change CDC’s overall assessment of the immediate public health risk from H5N1 avian influenza, which remains low,” the CDC said in a statement.

Since April, 61 human cases of H5 avian influenza have been reported in the United States, mostly among dairy and poultry workers.

The Louisiana case shows that people with backyard chicken flocks, hunters and other bird lovers should take precautions, the CDC said.

“The cases across the US are a constellation of spillover effects,” said Dr. Rebecca Christofferson, a virologist at the School of Veterinary Medicine at Louisiana State University. Experts still don’t understand exactly how these spillover effects occur and what specific factors increase a person’s risk.

“Right now it’s just kind of a black box with a lot of people trying to answer these questions,” Christofferson said.

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According to the CDC, the best approach is to avoid exposure. Infected birds can shed viruses through their saliva, mucus and feces, and other animals can shed them through their respiratory secretions and body fluids, including unpasteurized milk from cows.

“People who work with infected animals or come into recreational contact with infected animals are at higher risk of infection, and it is critically important that they follow CDC-recommended precautions when around infected or potentially infected people animals are located. We will continue to emphasize this message in light of the recent cases,” Daskalakis said.