The United States has recorded its first death from bird flu after a 65-year-old patient who was hospitalised on December 18 passed away.

The Louisiana Department of Health (LDH) announced the news on Monday. The patient had been the first person in the US to be hospitalised as a result of the virus, known as H5N1.

“LDH’s extensive public health investigation has identified no additional H5N1 cases nor evidence of person-to-person transmission. This patient remains the only human case of H5N1 in Louisiana,” the state agency said in a social media post. “Current general public health risk remains low.”

The Centers for Disease Control and Prevention (CDC) have confirmed 66 human cases in total in the US since April, though none as severe as the Louisiana case.

Authorities believe that the patient, who had pre-existing conditions, contracted bird flu through exposure to backyard chickens and wild birds.

While the risk to humans remains minimal so far, millions of birds and cattle have been killed in an effort to mediate the spread of the virus.

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The CDC says that most of the people who contracted bird flu in recent months have been exposed through their work with contaminated livestock and cattle.

An estimated 40 of the 66 cases have been linked to dairy herds, and another 23 have been traced to farms and culling operations.

“While the current public health risk for the general public remains low, people who work with birds, poultry or cows, or have recreational exposure to them, are at higher risk,” LDH said in a statement.

California declared a state of emergency over bird flu in mid-December after dairy cows in the western state tested positive for the virus. As of Monday, the CDC reported 701 confirmed cases in dairy cattle in California, out of a total of 917.

Many of the human cases of bird flu in the US have also been concentrated in California, which has a large agricultural sector. But no human-to-human transmission has been recorded. All but one of the cases in the state have been linked to cattle.

The CDC announced in late December that a genetic analysis of the Louisiana patient suggested that the virus had mutated inside the patient, which could allow the virus to better bind to receptors in the upper airways of humans.

Michael Osterholm, a University of Minnesota infectious disease researcher, told The Associated Press news agency that the development was concerning, but not dire.

“Is this an indication that we may be closer to seeing a readily transmitted virus between people? No,” Osterholm said. “Right now, this is a key that sits in the lock, but it doesn’t open the door.”

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The World Health Organization (WHO) said in a public health assessment in December that the impact of infections at the global level remained “minor”.