Medical Matters > Aetiology: Causation

ME Essential Autumn 2021


 Most people I know with ME say their illness started with or followed an infection – from which they never recovered. But there are a few who don’t recall a clear and sudden onset to their deterioration in health. So are we really sure that infections are always the cause of ME?


Patient and research evidence indicates that most people with ME/CFS, possibly around 75%, predate the onset of their illness to a very specific acute viral infection. A wide range of viruses are known to trigger ME/CFS. This includes common viral infections like Glandular Fever and Chickenpox through to more unusual tropical viral infections such as Ebola virus (in Africa) and Zicca virus (in South America).

Glandular fever (Epstein-Barr Virus) is a well-recognised trigger factor for post-viral fatigue syndromes in children and adolescents – where it is estimated to cause a prolonged post-viral illness or ME/CFS in around 10% of cases. Although far less common, nonviral infections can also trigger ME/CFS. Examples include giardia (which causes a nasty gastrointestinal illness) and Q fever (an illness caught from contact with sheep).

In some people, excessive physical or mental stress at the time of the infection appears to be an important co-factor in increasing the risk of developing ME/CFS. In a minority of cases, some other form of immune-system stressor – such as a vaccination, pregnancy, trauma or a surgical operation – appears to be the main triggering event. In the remainder, there is no clear triggering event with symptoms appearing more gradually.

In summary, it’s a complicated picture overall. In our current state of knowledge, my conclusion is that some form of significant stress on the immune system, often in the form of a viral infection, is the main factor in the development of ME/CFS in the majority of cases. In addition, as with conditions like heart disease and arthritis, some people might have a genetic predisposition to developing ME/ CFS when the right trigger factor comes along.

More information

What do you believe is primarily responsible for triggering your ME/CFS?

  • Bacterial infection 4.95%
  • Genetic susceptibility 4.37%
  • Hormonal imbalance 1.66%
  • Mental health 2.61%
  • Parasitic infection 0.43%
  • Pregnancy 0.62%
  • Stress 11.56%
  • Surgery 2.28%
  • Toxin exposure (pesticides etc.) 1.54%
  • Trauma (childhood trauma etc.) 4.74%
  • Vaccination (e.g., Hepatitis B) 15.19%
  • Viral infection 20.48%
  • It was something else entirely 1.69%
  • I don’t know what might have been the trigger 4.06%

If an infection, what type of infection do you believe was responsible?

  • Coronaviruses (e.g., Covid-19, SARS, or MERS) 1.17%
  • Dengue Fever 0.06%
  • Ebola virus 0%
  • Enterovirus (e.g., coxsackie B) 0.83%
  • Epstein Barr Virus (e.g., mono, or glandular fever) 11.62%
  • Giardia (parasite) 0.09%
  • Hepatitis A or B virus 0.09%
  • Human herpes virus (cytomegalovirus or herpes zoster) 1.08%
  • Human herpes 6 Virus (HHV6) 0.34%
  • Herpes simplex virus 1 (HSV1) 0.62%
  • Human Parvovirus B19 0.22%
  • Influenza virus A or B (The ‘Flu’) 2.95%
  • Meningitis (viral or bacterial) 0.77%
  • Pneumonia (streptococcus pneumoniae) (bacterial) 0.49%
  • Q Fever (Coxiella burnetii) (bacterial) 0.03%
  • Rhinoviruses (the ‘common cold’ viruses) 0.46%
  • Ross River Virus 0%
  • The infection is not listed above 3.01%

1881 votes (3252 answers)


Information provided by The ME Association should not be construed as medical advice. Don't assume any new or worsened symptoms are simply the result of having ME/CFS or Long Covid. We recommend that any information you deem relevant is discussed with your NHS GP as soon as possible. It is important that you seek personalised medical advice from the GP who is in charge of your care and who knows you well.

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