Health officials on Thursday said they don’t know how a Missouri person caught bird flu but believe it may be a rare instance of a “one-off" standalone illness.
Investigators trying to determine how the person caught the virus have not been able to confirm the exact strain of flu.
Centers for Disease Control and Prevention officials said the risk to the general public remains low. The Missouri case raised questions about the possibility of human-to-human bird flu transmission, but officials said there is no evidence of other people being infected.
“Right now, evidence points to this being a one-off case,” said Dr. Nirav Shah, CDC principal deputy director.
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Unusual flu strains that come from animals are occasionally found in people. This year alone, health officials identified seven human cases of swine flu in the U.S., officials said. But this is the first time the surveillance system detected an avian flu like this.
The H5N1 bird flu has been spreading widely among wild birds, poultry, cows and a growing number of other animals. Its growing presence in the environment increases the chances that people will be exposed, and potentially catch it, Shah said.
Citing patient confidentiality, health officials have disclosed few details about the Missouri case, which was first announced late last week.
The person had chest pain, nausea, vomiting, diarrhea and weakness and was hospitalized on Aug. 22 “for reasons related to their underlying medical conditions,” Shah said.
The patient was tested for flu as part of the treatment and was positive for influenza A, a broad virus category. Subsequent testing — completed last week — found the bug to belong to category of viruses usually seen in birds and not people. However, the patient had a very low concentration of viral genetic material, leaving officials without the ability to full analyze it and confirm exactly which virus it is, Shah said.
Partial genetic sequences from the virus in the Missouri patient were similar to the same segments in viruses isolated from U.S. dairy cows, CDC officials said.
"Ultimately, a full sequence may not be technically feasible," Shah said.
The patient had no known contact with dairy cows or other animals associated with the ongoing bird flu outbreak. The person later told Missouri health officials that they didn't drink unpasteurized milk or dairy products, Shah said in a Thursday call with reporters.
The patient received antiviral medication and has since recovered and gone home, health officials said.
As part of their investigation, officials hope to draw blood from people who were around the patient to see if they show evidence of infection, Shah said.
The Missouri patient was the 14th person in the U.S. sickened with bird flu since March, when the virus was detected in cows. One other person was infected in 2022. All of those cases were relatively mild illnesses, and each patient had been in direct contact with infected animals.
U.S. health officials have been making preparations for vaccines and other measures, in case the bird flu does start spreading widely among people or begins causing severe illness.
On Thursday, the CDC announced it is partnering with five commercial lab companies so they can develop and conduct tests for H5N1 or other viruses. The agency initially is devoting at least $5 million to the agreements, and making plans to scale up to $118 million over the next five years if necessary, Shah said.
In the past, CDC developed its own tests during the early stages of new epidemics, with widespread testing not becoming available until later. That slowed detection of emerging infections.
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