By Jamie Gumbrecht and Brenda Goodman, CNN

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

The agency said Wednesday that the person was exposed to sick and dead birds in backyard flocks; this is the first US bird flu case linked to a backyard flock.

“It is believed that the patient that was reported by Louisiana had exposure to sick or dead birds on their property. These are not commercial poultry, and there was no exposure to dairy cows or their 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 their current condition. They instead referred all inquiries about the case to the Louisiana Department of Health, which is leading the investigation.

According to state officials, the patient is experiencing severe respiratory illness related to H5N1 and is hospitalized in critical condition. The person is older than 65 and has underlying medical conditions that increased their risk of flu complications, the Louisiana Department of Health said in an email to CNN.

This virus, D1.1, is the same type found in recent human cases in Canada and Washington state and detected in wild birds and poultry in the United States. It’s different from B3.13, the type detected in dairy cows, some poultry outbreaks and other cases in humans across the United States.

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

Bird flu has been linked with severe human illness and death in other countries, but no person-to-person spread has been detected.

“This case does not change CDC’s overall assessment of the immediate risk to the public’s health from H5N1 bird flu, which remains low,” the agency said in a statement.

In California, Gov. Gavin Newsom declared a state of emergency Wednesday over the continued spread of H5N1 bird flu in that state.

Newsom said the measure was necessary because, despite intense efforts to contain it, the virus had spread beyond the Central Valley to four dairies in the southern part of the state.

“This proclamation is a targeted action to ensure government agencies have the resources and flexibility they need to respond quickly to this outbreak,” he said in a news release. “While the risk to the public remains low, we will continue to take all necessary steps to prevent the spread of this virus.”

The emergency declaration will give state agencies greater flexibility with staffing and free up more funding for the response.

Of the 61 confirmed human cases of bird flu in the US this year, 34 have been in California. Nearly all of those have been in dairy farm workers, according to the CDC.

The Louisiana case shows that precautions should be taken by people with backyard chicken flocks, hunters and other bird enthusiasts, the CDC said.

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

“It’s just kind of a black box at the moment that a lot of people are trying to answer these questions on,” Christofferson said.

The CDC says the best approach is to avoid exposure. Infected birds can shed viruses in their saliva, mucus and feces, and other animals may shed them in their respiratory secretions and bodily fluids, including unpasteurized milk from cows.

“People who work with or have recreational exposure to infected animals are at higher risk of infection, and it’s extremely important that they follow CDC recommended precautions when around infected or potentially infected animals, a message that we will continue to magnify given recent cases,” Daskalakis said.

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