The cause of<unk>  is unknown. Genetic and physiological factors are thought to work together to precipitate and perpetuate the condition. A 2016 report by the Institute of Medicine states that<unk>  is a biologically based illness, but that the biologic abnormalities are not sensitive or specific enough to be useful as a diagnosis. Because it may begin as an influenza-like illness with a sudden onset, various infectious causes have been proposed, but evidence is insufficient to support such causation. Infections proposed include mononucleosis, Chlamydophila pneumoniae, human herpesvirus 6, and Lyme disease. Inflammation may be involved. Often, the illness will follow a viral illness, such as mononucleosis or gastroenteritis. Risk factors All ages, ethnic groups, and income levels are susceptible to the illness. The CDC states that Caucasians may be diagnosed more frequently than other races in America, but the illness is at least as prevalent among African Americans and Hispanics. A 2009 meta-analysis showed that compared with Caucasians, African Americans, and Native Americans have a higher risk of<unk> , though it specifically excluded other more common ethnicities worldwide, and it acknowledged that studies and data were limited. More women than men get<unk> . 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<unk>  occurs up to four times more often in women than in men. The illness can occur at any age, but most frequently in persons between the ages of 40 and 60.<unk>  is less prevalent among children and adolescents than among adults. Blood relatives of those who have<unk>  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<unk>  as a neurological disease in the ICD-11 for Mortality and Morbidity Statistics (ICD-11). Viral and other infections Post-viral fatigue<unk>  (PVFS) or post-viral<unk>  describes a type of<unk>  that occurs following a viral infection. A recent review found Epstein-Barr virus (EBV) antibody activity to be higher in patients with<unk> , and that a subset of patients with<unk>  were likely to have increased EBV activity compared to controls. Viral infection is a significant risk factor for<unk> , with one study finding 22% of people with EBV experience fatigue six months later, and 9% having strictly defined<unk> . A systematic review found that fatigue severity was the main predictor of prognosis in<unk> , and did not identify psychological factors linked to prognosis. One review found risk factors for developing<unk>  after mononucleosis, dengue fever including longer bed-rest during the illness, poorer pre-illness physical fitness, attributing symptoms to physical illness, belief that a long recovery time is needed, as well as pre-infection distress and fatigue. Similar risk factors have also been found following the bacterial infection Q-fever. The same review found biological factors such as CD4 and CD8 activation and liver inflammation are predictors of sub-acute fatigue, but not<unk> , however these findings are not generally accepted due to the use of the Oxford criteria in selecting patients. The CDC does not recognize attribution of symptoms as a risk factor. A study comparing diagnostic labels found that people labelled with ME had the worst prognosis, while those with PVFS had the best. Whether this is due to those with more severe or longer lasting symptoms results in a label with the description of ME, or if being labelled with ME adversely causes a more severe or prolonged illness is unclear.
Chronic fatigue syndrome
Hypothyroidism
Cancer-related fatigue
Idiopathic chronic fatigue
Da Costa's syndrome  Da Costa's syndrome  1
Exercise addiction
Medication phobia
Generalized anxiety disorder