New York, May 20 (IANS): Young adults who survived Covid-19, even with mild infections, are at increased risk of a serious post-Covid or "long haul" problem -- chronic fatigue syndrome, say researchers.

A recent review of three case studies by Johns Hopkins University researchers provides first evidence that one serious post-Covid problem may be myalgic encephalomyelitis/ chronic fatigue syndrome (ME/CFS) -- the complex, multisystem disorder previously known as chronic fatigue syndrome.

"In the three patients studied -- all of whom had confirmed or highly probable Covid-19 infections early in the pandemic -- we observed ME/CFS-like symptoms within the first two weeks of illness," said Peter Rowe, director at Johns Hopkins Children's Center and Professor of Paediatrics at the Johns Hopkins University School of Medicine.

"At six months following their illness, all three still met the criteria for being diagnosed with ME/CFS," Rowe added.

The three patients evaluated in the recent study, published in the journal Frontiers in Medicine, were a 19-year-old man and two women, ages 22 and 30, whose Covid-19 symptoms began between April and June 2020.

Symptoms of orthostatic intolerance -- a group of clinical conditions that includes fatigue, lightheadedness and difficulty concentrating, and are linked with greater than 90 per cent of the people with ME/CFS -- were prominent in all three from the outset of their Covid-19 illness.

A six-month post-Covid symptom onset examination, including evaluations of movement, neurological function and continued orthostatic intolerance, was conducted on each of the patients to determine if ME/CFS could be diagnosed. All three easily met the criteria.

Interestingly, all three patients had relatively mild Covid-19 respiratory symptoms and none required hospitalisation, yet it appears to have translated into the more serious secondary problem of ME/CFS for them all, Rowe said.

Further research is needed to define the biological mechanism by which ME/CFS arises from Covid-19, and then use that insight to develop treatment strategies that can return patients with post-Covid ME/CFS back to their previous quality of life, the team said.