An individual in Louisiana has the first severe illness caused by bird flu in the United States, federal health officials said Wednesday.

The patient, who is hospitalized, had been in contact with sick and dead birds in backyard flocks on their property, the Centers for Disease Control and Prevention said. It’s the first case of H5N1 bird flu in the United States that has been linked to exposure to a backyard flock, and news of the infection comes the same day California officials declared a state of emergency to confront the outbreak spreading among dairy cows.

The Louisiana Health Department announced over the weekend that it had detected its first presumptive positive human case of bird flu in a resident of southwestern Louisiana who was hospitalized. The state provided no additional details initially.

Emma Herrock, a spokeswoman for the Louisiana Health Department, said in an emailed statement Wednesday the patient is over 65 and has underlying medical conditions. She declined to describe the person’s symptoms or severity of illness. Citing patient confidentiality, she said there would be no updates about the patient’s condition at this time.

People over 65 and individuals with underlying medical conditions are at higher risk of complications from influenza.

The case was confirmed by the CDC on Friday. In a briefing Wednesday, Demetre Daskalakis, a top CDC official, said preliminary genetic sequencing indicates the virus belongs to a version of bird flu recently detected in wild birds and poultry in the United States, and in recent human cases in British Columbia and Washington state.

That version, or genotype, is different from the one that has been detected in dairy cows, some human cases and some poultry outbreaks in the United States, he said. The patient had no exposure to dairy cows, and state officials are monitoring contacts and offering antivirals if needed.

Public health officials are watching this case carefully because in all of the other 60 cases of bird flu illness in the United States, patients have experienced mild illness, such as pink eye, or mild respiratory symptoms. They have all fully recovered, Daskalakis said. A teen in Canada was hospitalized with an H5N1 infection, and in that case officials have not been able to identify the source of exposure.

In the United States, there have been two cases — an adult in Missouri and a child in California — where health officials have not determined how they became exposed and infected.

In the past 25 years of global experience with the virus, of the more than 900 cases of H5N1 infection in other countries, infection has been associated with severe illness and — in about 50% of cases — death, officials have said.

Public health experts have been growing increasingly concerned about the spread of the virus in dairy herds in recent weeks, with more than 800 dairy herds infected in 16 states, with the more than 600 herds infected in California. The virus has also attacked poultry flocks and spread to other animals. On Wednesday, California Gov. Gavin Newsom declared a state of emergency “to streamline and expedite the state’s response,” he said.

For months, experts have warned that the longer the virus spreads among humans and animals, the greater the chance for mutations that make it more virulent and transmissible person to person. Scientists recently reported that it would take just a single mutation in the version of the bird flu that has swept through U.S. dairy herds to produce a virus adept at latching on to human cells, a much simpler step than previously imagined.

No person-to-person spread of H5N1 bird flu has been detected in any of the cases. The CDC said the latest case does not change the agency’s overall assessment of the immediate risk to the public’s health from bird flu, which officials said remains low.

But the virus is changing, said John Connor, an associate professor of microbiology at Boston University. “It is essentially going to the gym all the time and training to be better,” Connor said at a webinar on H5N1 this week hosted by Boston University’s Center on Emerging Infectious Diseases. “The virus is not just getting into birds, now it’s getting into cows. There’s evidence that it’s getting into other animals, cats, dogs, mink,” he said. “Now what we are seeing is that this is a virus that used to be only good at breaking and entering into bird cells and causing disease there and transmitting there, now its getting better at breaking and entering into a bunch of other cells.”

But he cautioned, “Right now we’re seeing a lot of breaking and entering in neighborhoods near us, but not our neighborhood.”

Health officials declined to share details about the Louisiana person’s symptoms and timeline of their illness for privacy reasons. On Monday, Louisiana sent a health alert to the state’s clinicians asking them to consider possible H5N1 virus infection in people with symptoms of acute respiratory illness or pink eye and who had exposure history within 10 days of the start of their symptoms. The state said it detected the presumptive positive case this past Thursday.

“The demonstrated potential for this virus to cause severe illness in people continues to highlight the importance of the joint coordinated U.S. federal response,” Daskalakis said at a news briefing.

The Louisiana patient’s illness was detected as part of existing surveillance for influenza. The patient was tested, based on their symptoms. When test results showed influenza A, subsequent testing was performed and identified H5N1, which is a type of influenza A, Daskalakis said.