A person in Missouri who has not reported any contact with animals has tested positive for H5 bird flu, the state Department of Health and Senior Services and the Centers for Disease Control and Prevention said Friday. It is not yet clear whether the person was infected with the same virus strain that is causing the ongoing outbreak among dairy cattle.
The person, who was hospitalized on August 22, had a number of underlying health conditions. The person has since recovered and been released, the state said his statement.
That’s what the CDC said this is the first case of H5 bird flu detected through the country’s national flu surveillance system, and the first H5 case in a person with no occupational exposure to infected cows or poultry.
A CDC spokesperson told STAT that analysis of the virus is still ongoing, but to date the agency’s scientists have seen no evidence of changes that would indicate the virus has evolved to become more transmissible to and between people.
While news of an H5 infection in a person with no known exposure to infected animals is alarming, experts who spoke to STAT cautioned that it is too early to jump to conclusions.
The thirteen other H5 cases reported this year were found during targeted surveillance of farmworkers exposed to infected animals, the CDC said. “In this case, the patient’s sample originally tested positive for influenza A, but negative for seasonal influenza A virus subtypes. That finding leads to additional testing.”
The CDC is working to generate and analyze a complete genetic sequence of the virus, if possible. At this time, the neuraminidase – the N number in the name of the virus – had not yet been determined.
Missouri has not reported any H5N1 outbreaks in dairy cattle. Fourteen states, including three in neighboring Missouri, have reported a total of 197 infected herds since the virus was first discovered in cows in late March. The state has reported some infections in poultry.
The CDC statement said no unusual flu activity is being observed in Missouri. And wastewater monitoring picked up no evidence of the H5 virus there.
It will be important to know if this is the same H5 virus causing the outbreak in cattle. There are multiple variants of H5 viruses in wild birds, and it is conceivable that this person was infected with a different strain of the virus, experts noted.
Florian Krammer, a flu virologist at the Icahn School of Medicine at Mount Sinai in New York, pointed out that earlier in May, a person in Mexico with no known contact with infected animals tested positive for H5N2another bird flu virus. The source of that person’s infection has not been detected. Such one-off cases occur occasionally, Krammer said.
Another possibility is that the individual consumed raw milk or a raw milk product that was infected with the virus. “It is something that you cannot rule out,” Krammer said.
The risk associated with drinking raw milk infused with the H5N1 virus is not clear, although tests have shown that contaminated milk makes mice seriously ill. Similarly, a number of farms with H5N1 in their cows have reported dead cats on their properties.
Tests conducted by the Food and Drug Administration and the U.S. Department of Agriculture have shown that pasteurization kills the H5N1 viruses in milk.
Michael Osterholm, director of the University of Minnesota’s Center for Infectious Diseases Research and Policy, raised the possibility that the individual in Missouri could have had contact with wild birds or their droppings, either while cleaning out a bird feeder or while handling a dead bird that a cat had collected.
Krammer said he wouldn’t be too concerned if any of these possibilities turned out to be the likely route of exposure for this person. “The problem would be if… this was a sign of low circulation [of the virus] among the population,” he said. “And we don’t know that and that is of course worrying.”
He suggested it will be important to test anyone around this person and in their community who has flu-like symptoms. “This must be taken seriously. I hope, and I think there is a good chance, that it is a one-time infection. But it’s not certain. We don’t know.”
Osterholm said he was encouraged by the lack of references in state and CDC news releases to possible further spread of the virus. Neither reported symptoms among contacts of the infected person or among health care workers caring for the person.
‘What we have is implicit, it is not stated. But it didn’t say anyone else was under investigation for possible illness,” he said.
Based on what is known so far, Osterholm said this new development has not increased his concerns about H5N1. “It doesn’t change what I think is the existing risk consideration,” he said.
This case is the 15th H5 infection detected in the United States, the 14th this year. (A case was discovered in Colorado in 2022 in a man involved in the cleanup of a poultry farm where infected birds had been culled.)
Of the previous cases this year, all have been directly or indirectly linked to the outbreak in cows. The cases — in Michigan, Colorado and Texas — involved dairy farm workers or people who were infected while working on poultry farms where the virus had spread.