A new study led by UCLA finds that rates of subsequent myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) following an acute illness were roughly the same between people whose acute illness was due to COVID-19 and those who did not have COVID-19.

Researchers of the large, multi-site study found a 3% to 4% prevalence of ME/CFS-like illness among study participants who tested positive for SARS-CoV-2 infection and the same prevalence in others who tested negative for COVID-19. The research was based on survey data collected three months to one year after patients' initial illnesses.

ME/CFS is a long-lasting, multi-system illness with no known cure or definitive cause. It is characterized by an inability to do activities that the patient could easily do before they became ill. This is often due to severe fatigue, trouble with cognition, and other symptoms that have a profoundly negative impact on daily living.

It's not known what causes ME/CFS but researchers and ME/CFS experts have suspected it may be tied to an infection, since many patients report an illness directly prior to developing ME/CFS symptoms.

"ME/CFS is no more likely to occur in people infected with COVID-19 than people with other acute illnesses," said Dr. Joann Elmore, a professor of medicine in the division of general internal medicine and health services research at the David Geffen School of Medicine at UCLA, and a co-senior author on the study.

"However, a 3 to 4% prevalence of ME/CFS after an acute COVID-19 illness would impose a very high burden on society and our health care system given the many millions of persons infected with SARS-CoV-2."

The findings are published July 24 in JAMA Network Open.

The study was conducted in English and Spanish under the umbrella of INSPIRE (Innovative Support for Patients with SARS-CoV-2 Infections Registry). It comprised 4,700 participants who experienced COVID-like symptoms between December 11, 2020 and August 29, 2022, with 68% of participants female.

The average percentage of participants with ME/CFS at three months was 3.4% for COVID-positive people and 3.7% for the COVID-negative group, with no significant differences in prevalence through 12 months of follow-ups.

The researchers note several limitations to the findings. Differences in participants' characteristics at baseline between the COVID-positive and -negative groups may not have been fully mitigated.

For instance, new COVID infections were more common in the months after the acute illness in the group that initially tested negative than in those who had tested positive at the beginning, and some people may not have been aware of a subsequent infection.

Also, there may have been false-positive and false-negative COVID test results, leading to misclassification of participants. Finally, assessment of ME/CFS is based on self-reported symptoms and may be subject to recall bias.