The Centers for Disease Control and Prevention estimates that between one million and four million Americans suffer from CFS. Those affected are often unable to perform at their normal level of ability. Bed rest does nothing to ease their problems. Increased physical activity often makes their symptoms worse.

CHRISTOPHER CRUISE: There is no test to confirm chronic fatigue syndrome.Instead, doctors use a patient's medical history and testing to dismiss other treatable conditions. Those who are confirmed to have the disorder must experience at least four of the symptoms of CFS for at least six months.

CFS was not widely accepted as a medical condition until the late nineteen eighties. Until then, many people who had it were said to be suffering from mental problems or stress.

It is not yet known what causes the disorder. Scientists have been studying the condition and debating its causes for hundreds of years. Some believe the cause is a viral infection.

FAITH LAPIDUS: Last month, experts urged America’s Food and Drug Administration to ban blood donations from people with a history of CFS. The experts noted conflicting results concerning a possible link between the disorder and a group of viruses known as murine leukemia viruses. MLVs are a kind of retrovirus known to cause cancer in mice. They include xenotropic murine leukemia virus-related virus, also known as XMRV.

Last year, researchers tested blood from thirty-seven patients with chronic fatigue syndrome. They also looked at forty-four healthy blood donors. They reported evidence of MLVs in eighty-seven percent of the CFS patients. This compared to seven percent of the healthy patients.