Oxford criteria

The Oxford criteria are a criteria for the diagnosis chronic fatigue syndrome published in 1991 by a group of psychiatrists. They identify two broad syndromes and are used primarily for research purposes.

Chronic fatigue syndrome

 * fatigue is the principal symptom: it is severe, disabling and affects physical and mental functioning; it should have been present for a minimum of 6 months during which it was present for more than 50% of the time.
 * other symptoms may be present: particularly myalgia, mood swings and sleep disturbances.
 * definite onset of symptoms, not life-long.
 * exceptions: patients with established medical conditions known to produce chronic fatigue; also patients with a current diagnosis of schizophrenia, manic depressive illness, substance abuse, eating disorder or proven organic brain disease.

Post-infectious Fatigue Syndrome (PIFS)
A sub-type of CFS which either follows an infection or is associated with a current infection (although whether such associated infection is of aetiological significance (i.e. whether it is the cause of the symptoms) is a topic for research).

To meet the research criteria for PIFS patients must:
 * i. fulfil the criteria for CFS as defined above (i.e. the Oxford definition)
 * ii. should also fulfil the following additional criteria:
 * (a) There is definite evidence of infection at onset or presentation (a patient’s self-report is unlikely to be sufficiently reliable).
 * (b) the syndrome is present for a minimum of 6 months after onset of infection.
 * (c) the infection has been corroborated by laboratory evidence.