Epidemiology of myalgic encephalomyelitis and chronic fatigue syndrome

Worldwide, an estimated 15 to 20 million people have myalgic encephalomyelitis. It is more prevalent in women than men and affects children as young as X and adults as old as X. In 80% of causes, the onset follows an acute infection.

Incidence and Prevalence
The prevalence rate is projected at 0.2% -0.4% although estimates vary widely due to different definitions and sampling methods used.

Estimated incidence rates – generally, the number of new cases in a single year – vary from 0.025% to 0.3% of the population.

Sex
Numerous studies have found the rates of ME/CFS to be substantially higher in adult women than in men, with estimates ranging from 75-85%.

A higher preponderance of women has also been noted in numerous outbreaks including Los Angeles, Akureyri, Rockville, MD, Royal Free Hospital, and Punta Gorda, Florida. In some cases, this was thought to do with the occupational hazard of nursing, but this female-skewed sex ratio was also found in several outbreaks among the general population. However, in other outbreaks, including the 1949-1953 Adelaide outbreak and an outbreak in northern England in 1955, a 1:1 gender ratio was reported. In Akureyri, a significantly higher incidence rate was found among adult women but not in patients under twenty.

Age
New cases of myalgic encephalomyelitis have been in children as young as eight and adults in their eighties. In terms of incidence, a study in Norway found two age peaks, one between 10 and 19 years and a second peak between 30 and 39 years. In terms of prevalence, Jason found that individuals in the 40- to 49-year-old age range exhibited the highest prevalence rates of CFS.

Race and ethnicity
In 1999, a community-based study by Dr Leonard Jason, et al, performed in the Chicago area found that individuals who identified as people of color exhibited higher rates of CFS than whites, with Latino participants demonstrating the highest CFS prevalence.

Socioeconomic characteristics
The prevalence of CFS was highest among skilled workers and lowest among professionals.

Severity


People with ME/CFS are more disabled and socially marginalized than for most other chronic illnesses.

Around 25 per cent of people with ME/CFS will have a mild form and be able to get to school or work either part-time or full-time, while reducing other activities. About 50 per cent will have a moderate to severe form of ME/CFS and not be able to get to school or work. Another 25 per cent will experience severe ME/CFS and have to stay at home or in bed.

In the US, 50-75% of patients with ME/CFS cannot work.

Genetics
5% of children of mothers with ME/CFS later developed the illness.

Infection
Infection is a major risk factor for the development of post-viral fatigue syndrome, chronic fatigue syndrome, and myalgic encephalomyelitis.

Prognosis
On average, many people with ME/CFS will improve in the first five years, but others may mainly stay at home or in bed, or may suffer relapses throughout their lives.

Mortality
One study found no increased risk of all cause mortality or mortality from cancer but an increased risk of suicide. Suicide risk was increased 6.85 compared to the general population. It was based on a cohort that used multiple clinical criteria, including the Oxford criteria. A Spanish study found a suicide risk of 12.75% versus 2.3% in the general population.

A 2006 study by Leonard Jason found that ME/CFS patients died of cancer, heart failure and suicide at considerable younger age than the general population. For example while the median age of death for cancer in the US was 72, the average age at which ME/CFS patients died of cancer was 47. And while the average age of heart failure in the general population was 83, it was only 58 in the ME/CFS sample.

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 * Pediatric
 * Prognosis