The rash in EBV (infectious mononucleosis) is most famously triggered by the administration of ampicillin, a specific historical clue not associated with CMV.
The acute retroviral syndrome of HIV can cause a rash, but it is often accompanied by prominent mucosal ulcers and a history of high-risk exposure.
Measles is distinguished by its prodrome of cough, coryza, and conjunctivitis, and the presence of Koplik spots inside the mouth before the rash appears.
The rubella rash is a finer, pinker maculopapular eruption that starts on the face and spreads down more rapidly, and is characteristically associated with posterior auricular lymphadenopathy.