Epidemiology of myalgic encephalomyelitis and chronic fatigue syndrome

Epidemiology of myalgic encephalomyelitis and chronic fatigue syndrome:

Statistics on the prevalence of myalgic encephalomyelitis and chronic fatigue syndrome vary. The CDC estimates that one million people in the US have ME/CFS and as many as 17-24 million people worldwide have ME/CFS. A recent UK biobank study places that estimate at 30 million. In 2015, the Institute of Medicine Report estimated there were between 836,000 and 2.5 million ME/CFS patients in the United States. 90% of patients are not diagnosed.

Twenty-five percent of ME/CFS patients have a very severe form of it. This 25% of patients are severely ill and are either bed-bound, wheelchair bound, or are housebound or nearly so.

ME/CFS is more prevalent in women than men, can affect children or adults but is most common in adults between the ages of 30 to 50 years old, or ages 40-60 in the United States. In 72% of causes reported by ME/CFS patients, the onset follows an acute infection, for example a virus or bacterial 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 ME/CFS 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 chronic fatigue syndrome (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 percent 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 percent will have a moderate to severe form of ME/CFS and not be able to get to school or work. Another 25 percent 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
Five percent of children of mothers with ME/CFS later developed the illness.

Infection
Infections are a risk factor for the development of ME/CFS. The vast majority of people diagnosed with ME/CFS report that their illness began after a virus or other infection, especially Epstein-Barr virus, Ross River Virus and Q fever.

Bodily response to physical or emotional stress
An accident, physical trauma, anaesthetics, or significant emotional stress have been reported by some patients prior to onset of symptoms. According to the CDC, this may cause a physical response by affecting body chemistry including the HPA axis, levels of corticotrophin-releasing hormone (CRH), the stress hormone cortisol and others.

Environmental factors
Mold or toxin exposure is an expected trigger although specific environmental factors with ME/CFS have not been established.

Prognosis
The prognosis for ME/CFS is considered to be poor with only a minority (a median estimate of 5%) returning to pre-morbid levels of functioning. The majority of patients remains significantly impaired. A substantial improvement however is noted in an estimated 40% of patients and the prognosis in adolescents is considered to be better than in adults.

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.