Research

Existing estimates of ME/CFS prevalence and their limitations

Although the exact prevalence of ME/CFS is unknown, several estimates exist both for the UK and elsewhere in the world. While not an exhaustive review of all studies containing information on ME/CFS prevalence (which would need to be a specific type of study that uses repeatable methods to search for, select, and combine all available evidence to answer a specific question; i.e. a systematic review), the following summarises key prevalence estimates, alongside the strengths and limitations of the methods used to calculate them.

Existing estimates for the UK – what do government reports and guidelines say?

The most frequently used estimate for the prevalence of ME/CFS in the UK is probably that cited in the information to the public relating to the 2021 NICE guidelines for diagnosing and managing ME/CFS, this states that ME/CFS:

 “affects about 250,000 people in the UK

However, even within the NICE guideline, inconsistency in the prevalence of ME/CFS can be observed; in the guideline itself – rather than the information to the public – it is stated that: 

“Recent data from the UK Biobank suggest that there are over 250,000 people in England and Wales with ME/CFS, with about 2.4 times as many women affected as men.”

This estimate of 250,000 people with ME/CFS came from research published in 2018 using data from the UK Biobank – “a large-scale biomedical database and research resource containing de-identified genetic, lifestyle and health information and biological samples from half a million UK participants”.

Findings showed that among 452,264 individuals in the UK Biobank, 1,829 people self-reported “CFS” – corresponding to a prevalence of 0.448%. Regrettably, the cases of CFS were self-reported and not assessed against any ME/CFS diagnostic criteria. Additionally, the UK Biobank data lacks ethnic diversity and only includes adults aged between 40 and 69 years between 2006 and 2010. These limitations mean that it may not be appropriate to extrapolate the prevalence of 0.448% to the wider UK population, as was done in the 2021 NICE guidelines.

Prevalence estimates also exist for Scotland and Northern Ireland:

A report from the Scottish Government on “Myalgic Encephalomyelitis/Chronic Fatigue Syndrome NICE guideline: stakeholder review” published in July 2022, stated that:

“Around 20,000 people in Scotland are living with the condition.”

Information from the “ME/CFS in Northern Ireland Position Statement as at 31 August 2016” suggests that:

“Specifically, there are more than 7,000 cases in Northern Ireland, with 10% of patients suffering from moderate to severe symptoms.”

While it is unclear exactly where the estimates for Scotland and Northern Ireland are obtained from, there is a reference to the idea that “a population prevalence of at least 0.2% to 0.4% is widely accepted” in the 2022 report from the Scottish Government – this range was also cited in another report from the Scottish Government first published in 2010, and updated in 2023. Regrettably, the position statement from Northern Ireland references a web page that can no longer be accessed.

Prevalence figures were also in circulation before the 2021 NICE guideline. The 2006 Gibson Report (Inquiry into the status of CFS / M.E. research into causes and treatment) quoted that the Chief Medical Officer’s (CMO) Report of 2002 stated:

“There could be anything from 100,000 to 250,000 people suffering from CFS/ME in the UK.”

Both the CMO Report of 2002 and the 2007 NICE guideline for ME/CFS utilised “a population prevalence of at least 0.2% – 0.4%” – although again did not provide a clear reference for this range (it is possible that the justification in the CMO report was published in an Annex which is no longer available online via the link provided in the report).

Although 0.2% to 0.4% is a wide range, it was considered by some as a “low estimate” and, of course, does not and could not predict the impact of long COVID on potential numbers of those capable of receiving a diagnosis of ME/CFS.

Considering a prevalence of 0.2% to 0.4% and applying it to the UK population at dates of quoted reports and guideline release dates:

YearPopulation0.2% of population0.4% of population
200259,365,677118,731237,462
200660,827,067121,654243,308
200761,319,075122,638245,276
202167,026,292134,052268,105

There have been no more recently published reports or guidelines that include information on the prevalence of ME/CFS in the UK. Thus to 2007, the 0.2% to 0.4% rate would, at the highest limit, be in accord with the 250,000 figure, but as population figures have risen the crude population range has exceeded 250,000; if the range of 0.2% to 0.4% is applied to the most recent population estimate for the UK – 68,265,200 people in 2023 – it would equate to between 136,512 and 273,025 people.

What does the research tell us?

Regrettably, there have been no peer-reviewed studies that provide estimates of the prevalence of ME/CFS in the UK since the UK Biobank study in 2018 – the study cited by NICE in 2021 as a reference for the 250,000 figure. Before this, a systematic review by Lim and colleagues, which included all research relating to the prevalence of ME/CFS published between 1990 and 2018, suggested that research using populations from the UK (not all UK-wide studies) provided a ME/CFS prevalence range of between 0.1% and 2.62% for the UK (another review by Estévez-López and colleagues published in 2020 identified that this range was 0.1% to 2.2% in Europe between 2002 to 2011).

Importantly, research published before 2018 has identified that prevalence rates for ME/CFS differ depending on which criteria are used. For example, the systematic review of international evidence by Lim and colleagues suggested that the prevalence of ME/CFS could lie anywhere between 0.04% (the lower range when considering evidence relating to the “Canadian Consensus Criteria; Epidemiological case definition; Post-viral exhaustion syndrome; and the National Institute for Health and Care Excellence guideline 2007”) and 12.55% (the upper value based on the Australian diagnostic criteria).

Since 2018, few studies have been published on the prevalence of ME/CFS. Notably, there has been one pre-print paper relating to the prevalence of ME/CFS in the UK. This study suggests a prevalence rate of 0.585% based on data for England – which the researchers state would equate to 390,195 people with ME/CFS in the UK based on the population size for 2022. However, the authors acknowledge that this is likely to be an underestimate of the true prevalence of ME/CFS as the data used to calculate the estimate only reflects diagnoses recorded in hospital records.

Elsewhere in the world:

  • A peer-reviewed study in Australia identified a prevalence rate of 0.095% for “A diagnosis of “myalgic encephalomyelitis”, “chronic fatigue syndrome”, “ME”, “CFS”, or “ME/CFS” but recognised that this was likely to be an underestimation due to delays in diagnosis and lack of interaction with health professionals.
  • A pre-print study in Canada suggested a prevalence of 0.4% for “confirmed cases of ME/CFS”, and 1.1% for self-reported cases of “CFS”.
  • A report by the Centers for Disease Control in the USA, published in 2023, found a prevalence of 1.3% for self-reported diagnosis of ME/CFS.
  • Peer-reviewed research from the USA, led by Mariah Wood and published in 2024, identified that among 2,745,374 adults in 2022, 45,892 (1.67%) reported symptoms consistent with the 2015 IoM criteria for ME/CFS – something the authors termed “ME/CFS-like illness”.

What about the impact of long COVID?

Due to the overlap in symptoms between ME/CFS and long COVID, it is essential to consider how the COVID-19 pandemic may have affected the prevalence of ME/CFS. Overall, research suggests that although ME/CFS may be no more common following COVID-19 than other infections, the number of people who contracted COVID-19 – and then developed long COVID – may mean that the number of those meeting ME/CFS diagnostic criteria (i.e. the prevalence of ME/CFS) has increased:

  • Research from Mariah Wood identified that 14.2% of the 45,892 adults in the USA who reported symptoms consistent with the 2015 IoM criteria for ME/CFS (or had ME/CFS-like illness”) developed the illness following COVID-19 infection.
  • Another study (behind paywall) from the USA by Mirin and colleagues, published in 2022, used existing ME/CFS prevalence estimates and concluded that if 10% of those with long COVID met ME/CFS diagnostic criteria, the prevalence of “ME/CFS” in the USA may have increased from 1.49 million to between “5 and 9 million individuals” – based on the 2022 population for the USA of 341.5 million, this would equate to approximately 1.46% to 2.64%, which includes the 1.67% observed by Wood and colleagues.

Summary

Although many studies have considered the prevalence of ME/CFS, no research accurately captures the proportion of people with ME/CFS in the UK in 2024. It is possible to use existing estimates and apply them to the UK population of today; for example, if the range 0.1% to 2.6% was applied to the most recent population estimate for the UK – 68,265,200 people in 2023 – these rates would translate to between approximately 68,265 and 1,774,895 people. Notably, this range includes the most recent estimate – from the pre-print study by Samms and Ponting – of 390,195 people with ME/CFS.

However, there are limitations of taking existing estimates and extrapolating to a different population. For example, these estimates do not capture the potential impact of long COVID on the prevalence of ME/CFS. The next article in this series will explore these limitations in more detail.

For more information on the limitations of studies included in this article, please read “Additional information on the studies relating to the prevalence of ME/CFS

What is prevalence? | Additional information | Difficulties with prevalence estimates | Summary

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