Chronic fatigue is an illness characterized by prolonged, debilitating fatigue and multiple nonspecific symptoms.

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Chronic fatigue syndrome (CFS) is an illness characterized by prolonged, debilitating fatigue and multiple nonspecific symptoms such as headaches, recurrent sore throats, muscle and joint pains, memory and concentration difficulties. Profound fatigue, the hallmark of the disorder, can come on suddenly or gradually and persists or recurs throughout the period of illness. Unlike the short-term disability of say, the flu, CFS symptoms linger for at least six months and often for years. The cause of CFS remains unknown.

The typical patient seeking medical care for CFS is a Caucasian woman in her mid-20s to late 40s. However, anyone at any age — male or female — can develop chronic fatigue syndrome, though cases reported in children under 12 are rare.

The illness was named chronic fatigue syndrome because it reflects the most common symptom — long-term, persistent fatigue. When the International CFS Study Group updated the definition of chronic fatigue syndrome in 1994, it decided to keep this name until a specific cause for the illness is discovered. (Today, chronic fatigue syndrome also is known as myalgic encephalomyelitis, postviral fatigue syndrome, and chronic fatigue and immune dysfunction syndrome.)

There are no published data to indicate that CFS is contagious, that it can be transmitted through intimate or casual contact or by blood transfusion, or that people with chronic fatigue syndrome need to be isolated in any way.

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