The Oxford criteria was published in 1991 and include both CFS of unknown etiology and a subtype of CFS called post-infectious fatigue syndrome (PIFS), which "either follows an infection or is associated with a current infection."
Oxfordski kriteriji su publicirani 1991. i uključuju oba SKU nepoznate etiologije i podvrstu SKU nazvanu post-infekcijski sindrom kroničnog umora (PIFS), koji „ili prati neku infekciji ili je asociran sa postojećom infekcijom“.