U.S. CDC Study Finds That H5N1 Human Infections Can Be Asymptomatic
Nikhil Prasad Fact checked by:Thailand Medical News Team Nov 03, 2025 7 hours, 1 minute ago
Medical News: Silent bird flu infections detected among humans
A major study conducted by researchers from the U.S. Centers for Disease Control and Prevention (CDC) has confirmed that some people infected with the deadly H5N1 bird flu virus can carry the infection without showing any symptoms. This means the virus can spread quietly among humans, making detection and containment more difficult for global health authorities. Since the first known human cases in 1997, more than 1,000 H5N1 infections have been recorded worldwide, mostly in individuals who had direct contact with infected poultry or wild birds.
U.S. CDC Study Finds That H5N1 Human Infections Can Be Asymptomatic
According to this
Medical News report, CDC scientists analyzed over 1,500 medical publications and identified 10 verified reports describing 18 cases of asymptomatic H5N1 infection. These cases included two individuals whose infections were confirmed through both molecular and serologic testing, while 16 others were confirmed only through molecular methods such as PCR testing. Researchers from the CDC in Atlanta, Georgia, led the investigation with collaboration from experts at the World Health Organization (WHO) and the Friedrich Loeffler Institute in Germany.
Where these silent infections were found
The two cases that met the highest level of confirmation occurred in Pakistan and Vietnam. In one of these cases, the person had direct exposure to infected chickens, while in the other, the infection was likely transmitted from another human. Neither person showed symptoms, and neither used any protective equipment. Other molecularly confirmed cases were reported in Bangladesh, Spain, the United Kingdom, Cambodia, and Vietnam, mostly among poultry workers or people living with infected individuals.
The CDC team emphasized that while these asymptomatic cases appear rare, they show that the virus can infect people without triggering any signs of illness. This hidden spread could complicate monitoring efforts and increase the risk of unnoticed transmission, especially in farming communities and regions with large-scale poultry production.
Growing global concern over bird flu’s reach
Experts from the Friedrich Loeffler Institute in Germany, which monitors animal health, have warned that Europe is seeing a surge in avian flu among poultry and wild birds, with over 30 farm outbreaks and 130 wild bird cases recently recorded. WHO virologist Klaus Stöhr cautioned that “the risk of the virus adapting to humans should not be underestimated,” adding that the current spread among birds provides many opportunities for mutation and human transmission.
Why this study matters
The study highlights that traditional surveillance, which relies on visible symptoms, may miss many infections. Scientists call for regular screening and blood testing of workers exposed to poultry or wild birds to detect silent cases early. They also stress the importance of determining whether asymptomatic individuals can pass the virus t
o others—a question that remains unanswered.
Researchers from the CDC concluded that ongoing monitoring, improved protective measures for poultry workers, and detailed studies of asymptomatic infections are essential to preventing future outbreaks. They warned that the true number of hidden infections might be higher than known and that early detection could help avoid another global health crisis similar to COVID-19.
The study findings were published in the peer reviewed journal JAMA Network Open.
https://jamanetwork.com/journals/jamanetworkopen/fullarticle/2840680
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Medical News.
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https://www.thailandmedical.news/articles/h5n1-avian-flu
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