Chronic fatigue syndrome
About 1% of primary-care patients have CFS; estimates of incidence vary widely because epidemiological studies define the illness dissimilarly. It has been estimated that 836,000 to 2.5 million Americans and 250,000 to 1,250,000 people in the United Kingdom have CFS. CFS occurs 1.5 to 2 times as often in women as in men. It most commonly affects adults between ages 40 and 60 years; it can occur at other ages, including childhood. Other studies suggest that about 0.5% of children have CFS, and that it is more common in adolescents than in younger children. Chronic fatigue syndrome is a major cause of school absence. CFS reduces health, happiness, and productivity; but there is controversy over many aspects of the disorder. Physicians, researchers, and patient advocates promote different names and diagnostic criteria; and evidence of proposed causes and treatments is often poor or contradictory.