A person in Missouri who didn’t report any contact with animals has tested positive for H5 bird flu, the state’s Department of Health and Senior Services and the Centers for Disease Control and Prevention said Friday. It’s not yet clear if the person was infected with the same virus strain that’s causing the ongoing outbreak among dairy cattle.
The individual, who had been hospitalized on Aug. 22, had a number of underlying health issues. The person has since recovered and has been released, the state said in its statement.
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 an individual without 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 suggest the virus has evolved to become more transmissible to and among people.
While news of an H5 infection in a person without known exposures to infected animals is unsettling, experts who spoke with STAT cautioned that it is too early to jump to any conclusions.
The 13 other H5 cases reported this year were found in targeted surveillance of farmworkers who had been exposed to infected animals, the CDC said. “In this case, the specimen from the patient originally tested positive for flu A, but negative for seasonal flu A virus subtypes. That finding triggers additional testing.”
The CDC is working to generate and analyze a full genetic sequence of the virus, if that is possible. At present the neuraminidase — the N number in the virus’ name — had not yet been determined.
Missouri has not reported any H5N1 outbreaks in dairy cattle. Fourteen states, including three that neighbor Missouri, have reported a total of 197 infected herds since the virus was first detected in cows in late March. The state has reported some infections in poultry.
The CDC’s statement said there is no unusual flu activity being detected in Missouri. And wastewater surveillance has not picked up evidence of H5 virus there.
It will be important to know if this is the same H5 virus that is causing the outbreak in cattle. There are multiple variations 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, an influenza virologist at Mount Sinai’s Icahn School of Medicine in New York, pointed out that earlier in May an individual in Mexico with no known contact with infected animals tested positive for H5N2, another bird flu virus. The source of that individual’s infection has not been detected. Such one-off cases occasionally happen, Krammer said.
Another possibility is that the individual could have consumed raw milk or a raw milk product that was infected with the virus. “It is something that you cannot exclude,” Krammer said.
The risk associated with drinking raw milk laced with H5N1 virus is not clear, though testing has shown that contaminated milk severely sickens mice. Likewise a number of farms with H5N1 in their cows have reported dead cats on their properties.
Testing conducted by the Food and Drug Administration and by the U.S. Department of Agriculture has shown that pasteurization kills 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 handling a dead bird that a cat had collected.
Krammer said he would not be too concerned if any of these possibilities turns out to be the likely route of exposure for this individual. “The problem would be if … this would be a sign of low-grade circulation [of the virus] in the population,” he said. “And we don’t know that and that is of course something that is worrisome.”
He suggested it will be important to test anyone in the vicinity of this individual, and in their community who has flu-like symptoms. “This needs to be taken seriously. I hope, and I think the chances are high, that it’s a one-off infection. But it’s not for sure. We don’t know.”
Osterholm said he was heartened by the lack of reference in the state and CDC press releases to any possible onward spread of the virus. Neither reported symptoms among contacts of the infected individual or health care workers who cared for the person.
“What we have is implied, it’s 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 amped up his concern about H5N1. “It doesn’t change what I think is the existing risk consideration,” he said.
This case is the 15th detected H5 infection in the United States, the 14th of this year. (There was a case detected in Colorado in 2022, in a man who was involved in cleaning up a poultry farm where infected birds had been culled.)
Of the previous cases this year, all have been linked, either directly or indirectly, to the outbreak in cows. The cases — in Michigan, Colorado, and Texas — have involved dairy farm employees or people infected while working on poultry operations where the virus had spread.