It’s said that 17 million people in the world have ME/CFS – but this figure is no more than a rough guess based on crude prevalence estimates from developed countries (0.2 to 0.4%, including children) applied to the 7 billion inhabitants of planet Earth! In fact, rigorous, robust estimates of the occurrence of the illness in each country are needed, particularly to plan healthcare and allocate funding for research.

In the UK, a team at the London School of Hygiene and Tropical Medicine have concluded an investigation which used rigorous methods to estimate the prevalence (numbers of people) and incidence (new cases each year) of ME/CFS. Their work was part of the ME/CFS Observatory, a collaborative National Lottery-funded research programme involving a series of investigations and the piloting of an ME/CFS specific disease register.

They examined a population of 143,000 people, aged 18 to 64 years, covered by primary care services in three English regions: London, East Anglia and East Yorkshire. Recruitment of patients followed a staged approach for the identification of cases, starting with a search of GP electronic databases, and ending with a clinical review and the classification of cases according to various definitions of ME and CFS, including the main CDC-1994 (Fukuda) and Canadian (2003) criteria. In their report, the overall minimal yearly incidence (new cases) was 0.015%, implying that potentially around 9,300 people develop the illness in the UK each year. Furthermore, the estimated minimum prevalence rate of ME/CFS was 0.2% , which accords with previous estimates and implies (all things being equal) that a minimum of 125,000 people are living with ME/CFS (however defined) in the UK. About half of these patients (0.11% or potentially 68,300 people) also met the more stringent Canadian definition, and they had more – and more severe – symptoms, including higher pain scores than patients who met the less restrictive Fukuda definition. Whether Canadian-defined patients represent a different clinical subgroup of “true” ME/CFS patients, or are simply ME/CFS patients with a greater burden of illness than others less severely affected, remains to be determined.

The use of a robust methodology, involving the employment of specific diagnostic criteria and rigorously sequenced filter procedures prior to the confirmation of cases, improves confidence in the estimates of the number of people with ME/CFS.

Reference: Prevalence of myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) in three regions of England: a repeated cross-sectional study in primary care. Nacul LC et al. BMC Med 2011 Jul 28; 9: 91.