From The New York Times:

Troubles of Chronic Fatigue Syndrome Start With Defining It

For an ailment with no known cause and subjective symptoms, definitions differ, and so do diagnoses.

When reports emerged 30 years ago that young gay men were suffering from rare forms of pneumoniaand cancer, public health investigators scrambled to understand what appeared to be a deadly immune disorder: What were the symptoms? Who was most susceptible? What kinds of infections were markers of the disease…

http://nyti.ms/gwBjgg