A Washington state resident become the first person in the world to die from a strain of virus that has never been seen before in humans.
The patient, an older adult with underlying conditions, was hospitalized with bird flu earlier this month after suffering from a high fever, confusion and severe breathing difficulties, officials said.
Lab tests confirmed the patient was infected with H5N5, a strain of bird flu previously detected in animals but never before recorded in people.
The person who died from the virus had a backyard flock of mixed domestic birds.
They were first treated by doctors in Grays Harbor County, about 100 miles west of Seattle, before being transferred to an unnamed hospital in King County in the Seattle area, for specialist care.
Before dying they were described as being 'severely ill'.
'The risk to the public remains low. No other people involved have tested positive for avian influenza,' the Washington State Department of Health said in a statement.
'Public health officials will continue to monitor anyone who was in close contact with the patient for symptoms to ensure that human-to-human spread has not occurred. There is no evidence of transmission of this virus between people.'
A Washington state resident has died from a strain of virus that has never been seen in humans before.
Avian influenza was detected within the flock making it likely the patient exposure to domestic poultry or wild birds the most likely source of the virus for the patient.
Further details about the patient, including their name, gender, age, and treatment, were not revealed.
It was not clear how the individual was infected, but officials said it was likely linked to exposure to wild or domestic birds.
Avian influenza was detected in the patient's backyard poultry flock, making it the likely cause of the infection.
Two of the birds in their flock died from an unidentified illness a few weeks ago, although the rest of the birds currently remain healthy.
Officials have followed up with individuals who had contact with the patient and tested those who had symptoms. There were no further cases of bird flu detected as of Friday, officials said.
It is possible to become infected with the virus after being exposed to saliva or droppings from infected birds or handling the body of a bird that died from the virus.
Where the strain could be determined, all previous human cases have been infected with the H5N1 strain.
Experts said the appearance of this strain in humans showed the virus's 'unpredictable' evolution. There is currently no evidence, however, that this strain is more infectious or severe in humans than other strains of the virus.
Officials at the Washington State Department of Health revealed the infection with a new strain of the virus last week.
The case marks the first bird flu infection detected anywhere in the US in at least eight months, and the first recorded in Washington state this year.
The case marks the first bird flu infection detected anywhere in the US in at least eight months and the first recorded in Washington state this year.
Since the bird flu outbreak began in January 2022, a total of 71 people have been infected, and one individual, a person in Louisiana, has died. Only four cases have been detected so far this year.
Officials have stressed, however, that the risk to the public remains low. Dr Beth Lipton, the state's public health veterinarian, said in a press conference: '[H5N5] is not a new strain or completely new virus. It is just the first time we know of that it has infected a person.'
Officials at the Washington State Department of Health revealed the infection with a new strain of the virus at a press conference on Friday.
Dr Angela Rasmussen, a virologist in Canada, warned on X: 'It's not H5N1, it's H5N5, but that isn't a relief to me. It's a reassortment that put someone in hospital. This is unpredictable.
'I hope epidemiologists are investigating to assess who else might have been exposed so appropriate outbreak investigation and control can be applied.'
Dr William Schaffner, an infectious diseases expert in Tennessee, told Newsweek: 'Infection with H5N5 bird flu virus likely is a rare one-off event that does not have widespread implications for general public.'
Since the bird flu outbreak began in 2022, most patients have been in either California which recorded 39 confirmed or probable bird flu cases or Washington where there were 15 confirmed or probable bird flu cases.
Officials have followed up with individuals who had contact with the patient and tested those who had symptoms. There were no further cases of bird flu detected as of Friday, officials said.
There is no current evidence that H5N5 is more likely to cause infections or severe disease in humans than other strains of bird flu.
In most cases, infections have been linked either to exposure to infected domestic poultry or dairy cows which have also been infected by the virus.
In wild and domestic birds, bird flu has now been detected in every state in the US since January 2022.
An estimated 174million wild and domestic birds are estimated to have been affected while more than 1,000 dairy herds have also been infected.
Since September this year, it has struck 7million farmed birds nationwide including 1.3million turkeys leading to concerns that there may be a shortage for thanksgiving.
Experts warn that infections with bird flu are more common at this time of year because wild birds which may be carrying the virus migrate potentially spreading the virus to new areas.
There remain concerns that the virus could spread to and learn how to spread between humans which could spark a new outbreak similar to the Covid pandemic.
The CDC says online that the risk to the public from bird flu remains low.
It says online: 'H5 bird flu is widespread in wild birds worldwide and is causing outbreaks in poultry and US dairy cows with several recent human cases in US dairy and poultry workers.
'While the current public health risk is low, CDC is watching the situation carefully and working with states to monitor people with animal exposures.
'CDC is using its flu surveillance systems to monitor H5 bird flu actively in people.'