My opinion is that they should have said infectious onset rather than viral.
From the paper:
Chronic fatigue syndrome (CFS) has been linked with exposure to several viruses and other infectious agents, with many onsets reported following primary infection with acute Mononucleosis, Lyme disease, and Q fever among others (
Komaroff, 2000). Additionally, acute infections by enteroviruses may persist in patients resulting in manifestations of CFS (
Chia & Chia 2008). Infection with or the reactivation of these viruses and possibly others (e.g., HSV-1, HHV-6, Epstein Barr virus, and Cytomegalovirus) may be involved the relapsing and remitting pathogenesis of CFS (
Englebienne & De Meirleir, 2002).
It seems very sloppy to include Lyme and Q fever as viruses.