A 21 year old college student presents to the emergency department with a rash.  Patient states that he has had a sore throat for the past 1 week for which he was recently prescribed amoxicillin by his PCP.  Over the past 1 day he has had progressively worsening rash over his body.  On exam you note a diffuse, erythematous, morbilliform rash.  What is the most likely infectious etiology of this patient’s pharyngitis?  (scroll down for the answer) 

A) Rhinovirus

B) Staph aureus

C) Haemophilus influenzae

D) Neisseria gonorrhoeae

E) Epstein barr virus

The correct answer is E) Epstein Barr virus.

Patients infected with Epstein Barr Virus who are treated with Ampicillin or Amoxicillin often develop a non-allergic, morbilliform rash. 

Epstein Barr Virus (EBV) Pearls

• Causative agent of heterophile positive infectious mononucleosis 
• Also associated with cancers: B cell lymphoma, Hodgkin’s disease, Burkitt’s lymphoma, Nasopharyngeal carcinoma 
• Transmitted via salivary secretions
• Infections in infants and young children are often asymptomatic or manifest as mild pharyngitis 
• Infections in teenagers and young adults can develop into infectious mononucleosis with fever, fatigue, lymphadenopathy, pharyngitis; over 50% of patients develop splenomegaly
• Complete blood count often helpful in diagnosis - can have lymphocytosis with greater than 50% lymphocytes and atypical lymphocytes on smear
• Monospot test identifies heterophile antibodies 
• Treatment centered around rest and analgesia, patient’s should avoid contact sports for a minimal of 3 weeks 

Stapczynski, J. Stephan,, and Judith E. Tintinalli. Tintinalli's Emergency Medicine: A Comprehensive Study Guide. 7th ed. New York, N.Y.: McGraw-Hill Education LLC., 2011.