Bird flu did not spread between humans in Missouri, tests show
Testing showed a Missouri bird flu patient did not infect the people around them, federal health officials said Thursday, a sign that the virus is not spreading among humans in a dreaded scenario that could trigger a new pandemic.
The virus, typically found in poultry farms, was discovered in dairy cows for the first time in the United States this year. Officials have confirmed 31 cases in humans – nearly all of whom worked on farms.
The Missouri case has been the most perplexing because the patient had no known exposure to animals that carry the virus, the first – and only – known U.S. case of a person who contracted the avian influenza strain known as H5N1 without working on a farm. Simultaneous symptoms experienced by a member of the patient’s household as well as the subsequent illnesses of six health care workers exposed to the patient triggered concern among disease detectives and public health experts of potential human-to-human transmission.
To find out, the Centers for Disease Control and Prevention conducted antibody screening on people exposed to that patient to test for a immune response consistent with a past H5N1 infection. Screening showed the person in the patient’s household who developed gastrointestinal symptoms on the same day had an antibody response to avian influenza, suggesting that they were exposed or infected. But health officials do not believe one infected the other because they developed symptoms simultaneously, and testing showed similar patterns in immune responses.
“They are all suggestive of positive infection caused by a common exposure, not person-to-person infection,” said Demetre C. Daskalakis, director of the CDC’s National Center for Immunization and Respiratory Diseases. The source of exposure remains unclear in both people.
Antibody screening ruled out H5N1 infection in five health-care workers who developed respiratory symptoms after encountering the patient. The sixth had previously tested negative. Health officials previously said those workers may have been infected with common respiratory viruses, such as the coronavirus.
Meanwhile, the CDC has deployed teams to help with investigations in California and Washington, where case counts in humans and animals have grown in recent days.
In California, a total of 137 dairy herds have tested positive and 15 humans, according to health officials.
Washington state recently became the sixth state to report human cases. The CDC confirmed two cases in workers exposed to infected poultry at a commercial egg farm and is conducting tests on five other workers who are presumed positive. The Washington workers reported mild symptoms, officials said.
About 800,000 birds were euthanized after test results on Oct. 15 showed that the flock was infected with avian influenza.
Nirav D. Shah, the CDC’s principal deputy director, said genetic testing suggests that the Washington poultry cases are unrelated to the outbreaks in dairy herds.
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Lena H. Sun contributed to this report.