Primary HIV infection causes a febrile illness that can closely resemble infectious mononucleosis. Most frequently, patients with acute HIV have fever, malaise, generalized lymphadenopathy, sore throat, headache, rash, and Gl symptoms The key distinctions between the two are that rash (unless antibiotics have been administered) and diarrhea are LESS common in infectious mononucleosis and tonsillar exudates are uncommon in primary HIV. It would be reasonable to check an HIV antibody test or plasma HIV RNA if his heterophile antibody test is negative