Blood tests of several people who had contact with a patient in Missouri who had contracted the H5N1 bird flu without any known exposure to infected animals show that at least one of them - a person who lived in the same house and had symptoms at the same time - had it virus as well, according to two sources with knowledge of the research.
H5N1 is a type of influenza that is rare in humans but highly contagious and fatal in several species, including poultry and dairy cattle, raising concerns that the virus could mutate and become one that also preys on humans.
The specialized blood tests, conducted by scientists at the U.S. Centers for Disease Control and Prevention in Atlanta, looked for immune proteins called antibodies that were produced in response to an infection. These antibodies confirm that a person has had an infection with a particular pathogen. The results were shared more widely with public health officials, scientists and the media Thursday morning during several calls hosted by health officials.
The tests were conducted to understand whether the Missouri patient - the first known person to contract the H5N1 flu in the United States without any apparent exposure to infected animals - has infected anyone else. Until now, the H5N1 virus has not been able to spread easily between people. Infectious disease experts fear that if the virus gains that ability, it could cause another pandemic.
While the results do not definitively rule out human-to-human transmission of the virus, they do suggest that it is not common or widespread and that it did not occur in a healthcare setting where healthcare providers have close physical contact with people. patients, CDC officials said. Although a person living in the patient's household was also positive, the CDC says the timing of their illness suggests both had a common exposure, rather than one contracting it from the other.
More than 20 people in the United States have tested positive for the H5N1 flu this year, and almost all of them have reported exposure to infected dairy cows or chickens, according to the CDC.
The source of the infections is still a mystery
The new test results show that the healthcare workers who developed symptoms of respiratory illness after caring for the patient - before doctors were aware of the H5N1 infection - were negative for antibodies against the infection. However, a person who lived in the same house with the patient and became ill at the same time did have antibodies against the H5N1 infection.
In a briefing Thursday, CDC officials explained that the household contact would not be counted as an official case because they did not test positive on at least two of the three methods of testing for infection accepted by the CDC and the World Health Organization.
Dr. Demetre Daskalakis, head of the CDC's National Center for Immunization and Respiratory Diseases, said the agency's tests were similar to the sonar on a ship trying to find something beneath the surface of the water.
"We know there is something down there and that the case and the household contact have likely been exposed to or infected with H5N1, but we cannot say whether what we see below the ocean surface is a whale or a submarine," said Daskalakis. .
Infectious disease experts with knowledge of the findings said it was a relief to see the results.
"I'm very reassured by the fact that the health care workers were not positive, and that gives me a lot more confidence that this is not really spreading among people in a sustainable way," said Dr. Jennifer Nuzzo, who is leading the pandemic response. Center at Brown University School of Public Health.
At the same time, Nuzzo said, information gaps limit what can be learned about how both the patient and a member of their household became ill.
Experts agree with the CDC's findings that because both people started experiencing symptoms at about the same time, it's more likely they shared a common exposure rather than one person giving it to the other, but say transmission of person to person in that case still cannot be completely ruled out.
"We still have all those questions," said Dr. Michael Osterholm, head of the Center for Infectious Disease Research and Policy at the University of Minnesota. 'Was it the same source? Was it person to person?"
Another question concerns the symptoms. Both people who tested positive for H5N1 did not have typical flu symptoms. Instead, they had gastrointestinal problems, including diarrhea, which initially led researchers to suspect that food poisoning might be the cause of their concurrent illnesses.
Osterholm said it is unclear whether the H5N1 virus caused these symptoms or if they may have had more than one infection at the same time.
"I've seen that happen before," he said.
Both the Missouri patient and his family member have been interviewed several times about possible exposure to the virus. Neither reported having any raw milk or other raw dairy products, and neither could recall any contact with potentially infected animals, including "direct or indirect contact with wild birds, domestic poultry, cats, livestock, including none consumption of raw dairy products, or other wildlife and close contacts," said Lisa Cox, spokesperson for the Missouri Department of Health and Senior Services, in an email. That agency led the investigation with help from the CDC.
Experts said the test results shed little light on how both people contracted the virus.
"I don't think we're going to get good data out of it that can tell us much," said Dr. Rick Bright, an immunologist and vaccine researcher who previously led the Biomedical Advanced Research and Development Authority.
Bright said it would be important to keep a bookmark in case similar cases come to light that could indicate the virus is causing unusual symptoms or perhaps infecting people through a route of exposure that has not yet been recognized.
"There are so many strange things about this case, I don't think we can put much stock in it," Bright said, although he added that the CDC has done a thorough job looking for antibodies in the case. He said the fact that health workers did not test positive was both "convincing and reassuring".
Look for evidence of previous infections
To get these test results, the CDC had to reconstruct the exact virus the Missouri patient was carrying, looking for antibodies that could attach to its unique structure. The agency explained in a recent news briefing that it is taking these additional steps to prevent false negative or false positive results.
The additional efforts increased the agency's confidence in its findings, but also added another delay to a case that took weeks to be identified and investigated. The patient was originally admitted to the hospital on August 22.
The delays, while perhaps unavoidable, have frustrated preparedness experts. They say any system that takes so long to identify and track infections will hamper the country's ability to respond if H5N1 infections become more widespread.
"I'm very happy that we are finally getting data that should have been shared weeks ago. I think that every case, every human case of H5 is an important case. They are all valid and they are all worth it [blood testing]because this is a virus that should not be in a human host and that we need to better understand so we can prevent potential human-to-human transmission," said Dr. Erin Sorrell, a senior scientist at Johns Hopkins University. Center for Health Security.
"Every data point is critical at this point in the process," Sorrell says. "So just that delay, I think, is a huge, huge problem."
On Thursday, health officials announced that H5N1 testing would soon be available through several commercial laboratory companies, including Quest Diagnostics. These tests would be available to patients with a doctor's prescription.
The CDC said it is working with health care providers to educate them about the circumstances that might qualify someone for bird flu testing, such as a dairy worker with symptoms of a bird flu infection.
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