Chronic fatigue syndrome epidemiology and demographics

Epidemiology
Due to problems with the definition of CFS, estimates of its prevalence vary widely. Studies in the United States have previously found between 75 and 420 cases of CFS for every 100,000 adults. The CDC states that more than 1 million Americans have CFS and approximately 80% of the cases are undiagnosed. All ethnic and racial groups appear susceptible to the illness, and lower income groups are slightly more likely to develop CFS. More women than men get CFS &mdash; between 60 and 85% of cases are women; however, there is some indication that the prevalence among men is underreported. The illness is reported to occur more frequently in people between the ages of 40 and 59. Blood relatives of people who have CFS appear to be more predisposed. However, CFS does not appear directly contagious; caretakers, partners and others in close contact with persons with CFS for years do not develop CFS any more frequently (excluding relatives, as earlier).

Epidemiological research on children and adolescents has received minimal focus according to a 2006 research review. Among minors, prevalence appears to be lower than for adults and various studies have found a range of 50-80% of the cases occur in girls. The authors hypothesize the differences in estimates of ME/CFS among pediatric studies may result because of the lack of a reliable pediatric case definition.

CFS generally occurs in endemic cases. In addition, over 50 instances have been documented, such as the Royal Free Hospital incident, where epidemic clusters were reported. In these instances, significant numbers of people came down with illnesses described as ME or CFS simultaneously, confined to a local area or even a single building. An infectious origin for these clusters was considered highly likely due to:


 * transference by inoculation to monkeys which developed symptomology and on post-mortem demonstrated neurological, vascular and cardiac damage (Fellow and Miles, 1955).


 * human post-mortems or scans demonstrating abnormalities consistent with chronic infection (Wallis 1957, Schwartz et al 1994)


 * serologic evidence of Iceland Disease blocking spread of polio type I spreading northwards (Sigurdsson et al, 1958).


 * the pattern of acute onset with pharyngitis, mild fever, muscular pain, neck stiff­ness, cervical lymphadenopathy, gastroenteric symptoms, diffuse CNS involvement and photosensitivity were consistent with viral infection with an observed incubation period of 5-7 days. The biphasic clinical picture echoes pathogenesis through the pharynx, spreading through the reticuloendothelial barrier, then the CNS, resulting in morphological changes in mature lymphocytes and antibody creation. (Acheson, Ramsay, Richardson, Crowley, Dillon et al)


 * A predilection for residential communities and most outbreaks occurring in summer (Acheson)


 * The isolation of the non-polio enterovirus ECHO-9 in patients (Lyle, Annals of Internal Medicine 1959; 51: 248-269)


 * psychiatric disease was a widely regarded exclusion for M.E. diagnosis (e.g. Acheson) and positive criteria for hysteria were absent (Gosling, Mayne, 1970).


 * At the 1978 RSM Symposium, new evidence was presented of increased anti-complementary activity and the ability of lymphocytes to proliferate and survive in vitro for up to 19 weeks. (Compston 1978).

Since most current definitions of CFS exclude such findings and signs, it is disputed whether they refer to a differential diagnosis (but see below).

According to the CDC, CFS itself is not contagious.