NEW YORK (AP) – Health officials have released the first nationally representative estimate of how many U.S. adults have chronic fatigue syndrome: 3.3 million.

The Centers for Disease Control and Prevention’s number is larger than previous studies have suggested, and is likely boosted by some of the patients with long COVID. The condition clearly “is not a rare illness,” said the CDC’s Dr. Elizabeth Unger, one of the report’s co-authors.

Chronic fatigue is characterized 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.

The condition rose to prominence nearly 40 years ago, when clusters of cases were reported in Incline Village, Nevada, and Lyndonville, New York. Some doctors dismissed it as psychosomatic and called it “yuppie flu.”

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

Doctors “called me a hypochondriac and said it was just anxiety and depression,” said Hannah Powell, a 26-year-old Utah woman who went undiagnosed for five years.

The new CDC report is based on a survey of 57,000 U.S. 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 percent said yes to both questions.

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

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 Center.

“It’s never, in the U.S., become a clinically popular diagnosis to give because there’s no drugs approved for it. There’s no treatment guidelines for it,” Dr. Clauw said.

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

Long COVID has been 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,” Dr. Brayden Yellman, a specialist at the Bateman Horne Center in Salt Lake City, Utah, said. But long COVID is more widely accepted by doctors, and is being diagnosed much more quickly, he said.

Ms. Powell, one of Dr. Yellman’s patients, was a high school athlete who came down with an illness during a trip to Belize before senior year. Doctors thought it was malaria, and she seemed to recover. But she developed a persistent exhaustion, had trouble sleeping and had recurrent vomiting. She gradually had to stop playing sports, and had trouble doing schoolwork, she 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 organization that helps domestic violence victims.

Getting care is still a struggle, she said.

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