"sufferers of other somatic or mental health conditions." I do have some concern over this, though for other reasons than discussed so far. They could have just said "other health conditions" and leave it at that. Instead they used "somatic" which is easily misinterpreted, and "mental" which does include somatoform disorders. Its clumsy language. I am however more sensitized to such language as I am looking for examples of this kind of thing.
It's also important to note that all of the researchers are from psychological or psychiatric departments at their institutions. They almost certainly intended to study CFS as a psychological disorder, barely even giving lip service to any comparison to physiological diseases.