Chronic fatigue is characterised by at least six months of severe exhaustion not helped by bed rest. Patients also report pain, brain fog and other symptoms that can get worse after exercise, work or other activity. There is no cure, and no blood test or scan to enable a quick diagnosis.

Doctors have not been able to pin down a cause, although research suggests it is a body’s prolonged overreaction to an infection or other jolt to the immune system.

Some physicians still hold that opinion, experts and patients say.

The new CDC report is based on a survey of 57,000 US adults in 2021 and 2022. Participants were asked if a doctor or other healthcare professional had ever told them they had myalgic encephalomyelitis or chronic fatigue syndrome, and whether they still have it. About 1.3 per cent said yes to both questions.

That translated to about 3.3 million adults, CDC officials said.

Among the other findings: the syndrome was more common in women than men, and in white people compared with some other racial and ethnic groups. Those findings are consistent with earlier, smaller studies.

However, the findings also contradicted long-held perceptions that chronic fatigue syndrome is a rich white woman’s disease.

There was less of a gap between women and men than some previous studies suggested, and there was hardly any difference between white and black people. The study also found that a higher percentage of poor people said they had it than affluent people.

Those misperceptions may stem from the fact that patients who are diagnosed and treated “traditionally tend to have a little more access to healthcare, and maybe are a little more believed when they say they’re fatigued and continue to be fatigued and can’t go to work”, said Dr Brayden Yellman, a specialist at the Bateman Horne Centre in Salt Lake City, in the US state of Utah.

The report relied on patients’ memories, without verifying their diagnoses through medical records.

That could lead to some overcounting, but experts believe only a fraction of the people with chronic fatigue syndrome are diagnosed, said Dr Daniel Clauw, director of the University of Michigan’s Chronic Pain and Fatigue Research Centre.

“It has never, in the US, become a clinically popular diagnosis to give because there [are] no drugs approved for it. There [are] no treatment guidelines for it,” Clauw said.

The tally probably includes some patients with long Covid who were suffering from prolonged exhaustion, CDC officials said.

Long Covid is broadly defined as chronic health problems weeks, months or years after an acute Covid-19 infection. Symptoms vary, but a subset of patients have the same problems seen in people with chronic fatigue syndrome.

“We think it’s the same illness,” Yellman said. But long Covid is more widely accepted by doctors, and is being diagnosed much more quickly, he said.

After five years, she was diagnosed with chronic fatigue and began to achieve some stability through regular infusions of fluids and medications. She graduated from the University of Utah and now works for an organisation that helps domestic violence victims.

Getting care is still a struggle, she said.

“When I go to the emergency room or to another doctor’s visit, instead of saying I have chronic fatigue syndrome, I usually say I have long Covid,” Powell said. “And I am believed almost immediately.”