A 2009 meta-analysis showed that African Americans and Native Americans have a higher risk of CFS, though it specifically excluded other more common ethnicities worldwide, and it acknowledged that studies and data were limited.More women than men get CFS. A large 2020 meta-analysis estimated that between 1.5 and 2.0 times more cases are women. The review acknowledged that different case definitions and diagnostic methods within datasets yielded a wide range of prevalence rates. The CDC estimates CFS occurs up to four times more often in women than in men. The illness can occur at any age, but has the highest prevalence in persons between the ages of 40 and 60. CFS is less prevalent among children and adolescents than among adults.Blood relatives of those who have CFS appear to be more predisposed, implying that genetic factors may increase the risk of susceptibility to the illness.According to the CDC, "CFS is a biological illness, not a psychologic disorder", and those affected "are neither malingering nor seeking secondary gain". The World Health Organization (WHO) classifies CFS as a neurological disease in the ICD-11 for Mortality and Morbidity Statistics (ICD-11). Viral and other infections
Post-viral fatigue syndrome (PVFS) or post-viral syndrome describes a type of chronic fatigue syndrome that occurs following a viral infection. A recent review found Epstein–Barr virus (EBV) antibody activity to be higher in patients with CFS, and that a subset of patients with CFS were likely to have increased EBV activity compared to controls.
For the majority of persons with CFS, work, school, and family activities are significantly reduced for extended periods of time. The severity of symptoms and disability is the same regardless of gender, and many experience strongly disabling chronic pain. Persons report critical reductions in levels of physical activity. Also, a reduction in the complexity of activity has been observed. Reported impairment is comparable to other fatiguing medical conditions including late-stage AIDS, lupus, rheumatoid arthritis, chronic obstructive pulmonary disease (COPD), and end-stage kidney disease. CFS affects a persons functional status and well-being more than major medical conditions such as multiple sclerosis, congestive heart failure, or type II diabetes mellitus.Often, courses of remission and relapse of symptoms occur, which make the illness difficult to manage. Persons who feel better for a period may overextend their activities, and the result can be a worsening of their symptoms with a relapse of the illness.About 25% of people with CFS are house-bound or bed-ridden for long periods during their illness, often for decades. : 32  An estimated 75% are unable to work because of their illness. More than half were on disability benefits or temporary sick leave, and less than a fifth worked full-time. Children who become ill with CFS are a major cause of school absence.