A persistent infection could explain why some people, but not others, develop long COVID symptoms, according to a new study led by researchers at the Brigham and Women’s Hospital. In a study of over 1,500 blood samples, the team found evidence of persistent infection in 43 percent of participants with cardiopulmonary, musculoskeletal or neurologic symptoms of long COVID.
Their study appears in Clinical Microbiology and Infection. The lead author is Zoe Swank, PhD, a postdoctoral research fellow in the Department of Pathology.
“If we can identify a subset of people who have persistent viral symptoms because of a reservoir of virus in the body, we may be able to treat them with antivirals to alleviate their symptoms,” said Swank.
The study analyzed 1,569 blood samples collected from 706 people, including 392 participants from the National Institutes of Health-supported Researching COVID to Enhance Recovery (RECOVER) Initiative, who had previously tested positive for a COVID infection.
With a highly sensitive test they developed, the Brigham researchers looked for whole and partial proteins from the SARS-CoV-2 virus. They also analyzed data from the participants’ long COVID symptoms, using electronic medical chart information or surveys that were gathered at the same time as the blood samples were taken.
Compared to people who didn’t report long COVID symptoms, those who reported persisting symptoms were approximately twice as likely to have SARS-CoV-2 proteins circulating in their blood. The research team was able to detect the spike protein and other components of the SARS-CoV-2 virus using Simoa, an ultrasensitive test for detecting single molecules. Commonly reported long COVID symptoms included fatigue, brain fog, muscle pain, joint pain, back pain, headache, sleep disturbance, loss of smell or taste, and gastrointestinal symptoms.
Specifically, 43% of those with long COVID symptoms affecting three major systems in the body, including cardiopulmonary, musculoskeletal, and neurologic systems, tested positive for viral proteins within one to 14 months of their positive COVID test. But only 21% of those who didn’t report any long COVID symptoms tested positive for the SARS-CoV-2 biomarkers in this same period.
It’s possible that a persistent infection explains some—but not all—of the long COVID sufferers’ symptoms. If this is the case, testing and treatment could aid in identifying patients who may benefit from treatments such as antiviral medications.
One of the questions raised by the study is why more than half of patients with wide-ranging long COVID symptoms tested negative for persistent viral proteins.
“This finding suggests there is likely more than one cause of long COVID,” said David Walt, PhD, a professor of pathology at the Brigham and Women’s Hospital and principal investigator on the study. “For example, another possible cause of long-COVID symptoms could be that the virus harms the immune system, causing immune dysfunction to continue after the virus is cleared.”
The idea that a virus can stay in the body and cause ongoing symptoms months after an infection isn’t unique to COVID. “Other viruses are associated with similar post-acute syndromes,” said Swank. She noted animal studies have found Ebola and Zika proteins in tissues post-infection, and these viruses have also been associated with post-infection illness.
