Millions of people worldwide may be suffering from long COVID without realising they have had the virus in the first place, according to a study.
That means that people with post-viral symptoms such as fatigue and brain fog could be missing out on the right treatment, researchers have warned.
Scientists studied a small group of people with post-viral syndrome and found that their immune responses showed that 41% had evidence of SARS-CoV-2 exposure.
Millions were exposed to SARS-CoV-2, the virus that causes COVID-19, early in the pandemic but could not get diagnosed due to testing limitations.
Many of those people developed a post-viral syndrome with symptoms similar to those of long COVID.
Study author Igor J Koralnik, of Northwestern Medicine Comprehensive COVID-19 Center in Chicago, said: "Since most long COVID clinics are only accepting patients with a positive test result, these people experiencing identical symptoms are left without specialised care and excluded from research studies on long COVID.
"Our data suggest that millions... with post-viral syndrome may have been exposed to SARS-CoV-2 at the beginning of the pandemic, and they deserve the same access to care and inclusion in research studies as people with a confirmed COVID diagnosis."
The study involved 29 people with post-viral syndrome, including neurologic symptoms such as problems with memory and thinking skills, headache and fatigue, but who did not have a positive COVID test result.
They were matched with 32 people of similar age with long COVID and positive test results. Both groups were also compared to 18 people with none of those symptoms and no known exposure to COVID or positive test result.
Researchers tested the participants for antibodies to two types of proteins that show an immune response that indicate a prior COVID infection.
Of the 29 people with post-viral syndrome, 12 people, or 41%, had immune responses consistent with prior exposure to COVID and similar to the long COVID group.
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