Infectious mononucleosis

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  • Caused by Epstein-Barr virus
    • CMV and HHV-6 may cause mononucleosis-like illnesses

Clinical Features

  • Triad of:
    • Fever
    • Pharyngitis
    • Lymphadenopathy
  • Symptoms
    • abrupt or insidious, ha, fever & malaise common w/ st & lad to follow
    • Rash in 10-15% usu btwn 4th-6th day of illness
      • red macular or maculopapular morbilliform rash of trunk & upper arms
      • occ involves face, thigh & legs, periorbital & eyelid edema in 50% of cases
  • Previously treated at strep throat
    • Morbilliform rash can develop[1]
      • 95% of patients on amoxicillin or ampicillin
      • 40-60% with other beta-lactams


  • Heterophile antibody (monospot) test
    • Up to 25% of pts in 1st week of symptoms may have false negative test
    • 10% of pts w/ EBV infection will be persistently negative
  • Amoxicillin reaction
    • Amoxicillin in pt w/ EBV will cause maculopapular rash in most
  • Definitive testing for suspected Mono during pregnancy (to r/o other pathology)
    • Send for: Epstein Barr virus, cytomegalovirus, and HIV

Differential Diagnosis

Acute Sore Throat

Bacterial infections

Viral infections



Pediatric Rash


  • Supportive



  1. Luzuriaga K and Sullivan JL. Infectious mononucleosis. N Engl J Med. 2010; 362:1993-2000.
  2. Melio, Frantz, and Laurel Berge. “Upper Respiratory Tract Infection.” In Rosen’s Emergency Medicine., 8th ed. Vol. 1, n.d.