This study investigates whether there is an immune response directed against gut microbes or food and parts of the body in severe Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) patients.

Severe Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) patients will be identified by Epsom and St Helier CFS Service and the Clinical Research Network Eastern. Information sheets will be posted by health professionals to eligible patients. Interested patients are asked to arrange a telephone call with the research team to receive more information about the study. Volunteers still interested after the 72 hour consideration period arrange a home visit to be taken through the consenting process.

Household controls will be recruited through patients participating in the study. Patients invited will be provided with information about household controls. The patient identifies and informs potential household controls of the study using information sheets provided by their health professional. Household controls willing to participate in the study will be taken through an eligibility questionnaire with GCP trained researchers.

Six stool and blood samples will be collected over the three year study period. Stool and blood samples need to be collected within 24 hours of each other, during home visits. 48 hour food diaries will be completed prior to each stool sample collection.

The study is based at the Quadram Institute and the University of East Anglia (UEA). The research is funded by the UEA and Invest in ME Research UK.

Inclusion Criteria:

• severe ME/CFS patients: men or women aged 18 to 70 years with a clinical diagnosis of severe ME/CFS patients
• household controls: men or women aged 18 to 70 years, no current or on-going medical conditions. Has to be either related/non-related, living in the same household or in close proximity to, or providing care to the severe ME/CFS patient they are paired with.

Exclusion Criteria:

• severe ME/CFS patients: the presence of significant anxiety or depression. Have received probiotics or antibiotics up to six weeks before joining the study.
• Household controls: The presence of long term medical conditions, in particular, affecting the stomach or bowel. Previously diagnosed with autoimmune diseases, for example, systemic lupus erythematous or rheumatoid arthritis. Suffer from significant anxiety or depression. In recipient of immunomodulatory drugs, statins, beta blocker or steroids. Have received probiotics or antibiotics up to six weeks before joining the study.

Severe ME/CFS patient attending Epsom and St Helier CFS Clinic will be identified by the Director of the clinic, Dr Bansal. CRN Eastern will notify general practitioners and occupational therapists of the study. They will then identify severe ME/CFS patients in the East of England.

Household controls will be recruited through severe ME/CFS patients participating in the study.