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Beth Unger: Epidemiology of CFS–what have we learned?

She started by saying that there is often disagreement about terminology and definition, which can be confusing. I.e., Are CFS and ME synonyms or different?

There is consensus that the illness is characterized by severe fatigue unrelieved by rest, and accompanied by additional symptoms, such as post-exertional malaise and cognitive difficulty, etc. There may be other comorbid conditions. The key issue is the vicious circle of sleep, pain and fatigue leading to cognitive difficulties.

The areas of disagreement in the definitions seem to be duration, number of symptoms, exclusion conditions and whether post-exertional malaise is acquired or part of the disease. Most studies are based on the 1994 Fukuda definition and this is widely used. The findings can be extrapolated to other definitions. 80% of patients do have post-exertional malaise. Case definitions are inadequate to explain the actual experience of the illness. Patients and caregivers do however speak eloquently.

Epidemiology looks at demographics, prevalence, significance, prognosis and risk factors.

Prevalence: The highest prevalence is in the 40-50 year old age group. More females than males are affected. It does occur in children. Prevalence may be higher in some racial groups and the socially disadvantaged. Most CFS patients are ill for more than 5 years. 50% seek medical care.

When finding out how common the illness is, it depends where you look and how you ask. A meta-analysis of 14 adult studies showed a different picture with self-report of 3.2% and clinical assessment at 0.76%. Prevalence is likely about 0.31% in the USA, which equates to about 1 million sufferers. In teens the rate is between 0.4% and 2.4%. it is not rare.

Significance: Functional impairment is equivalent to that in MS, HIV, cancer, diabetes and lung disease. There is frequently inability to attend school. There is decreased working memory and motor speed. Various domains of the SF36 generate generally low scores. For fatigue, sleep and pain, the PROMIST scores are worse compared to other illnesses.

Economic burden: In the USA, $9-37billion is lost in productivity, (equivalent to 19% reduction in earnings) and $9-14billion in medical costs.

Barriers to healthcare utilization: Over half the patients had at least one barrier. These included: accessibility, negative illness beliefs, the healthcare system itself.

Prognosis: Presentation of the illness may be sudden or gradual, and symptoms wax and wane. Good clinical management leads to increased wellbeing and functional improvement. The likelihood of recovery decreases with the severity of the illness. Recovery is more likely in children.

Associated factors: Infection, stressors, genetics. Work is usually done using case definitions as there is no biomarker. It is important to identify subgroups.

Future directions include: a multi-site study of CFS/ME and exploring the use of national surveys.