Rationale: Several primary viral infections have similar presentations. Fever, malaise, and lymphadenopathy are common symptoms. CMV is frequently associated with liver involvement. A maculopapular truncal rash can often be seen in primary HIV infection. Oral ulcers are commonly seen with primary HSV infection. Infectious mononucleosis may have associated splenomegaly and, in particular, a severe sore throat. Secondary syphilis is often characterized by a rash that also involves the palms and soles. As seen above, symptoms, signs, and epidemiology (e.g., host risk factors) are helpful in suggesting an infectious etiology, but laboratory investigation is needed for confirmation of the clinical diagnosis.