Mononucleosis (EBV)

A college freshman with a sore throat and fatigue gets prescribed amoxicillin for 'strep' — two days later they're covered in a rash. The antibiotic didn't cause an allergy. It unmasked the real diagnosis.

Infectious mononucleosis is caused by Epstein-Barr virus (EBV), transmitted via saliva — hence 'the kissing disease.' It is most common in adolescents and young adults. Classic presentation: the triad of profound fatigue, fever, and exudative pharyngitis, plus posterior cervical lymphadenopathy and splenomegaly. Atypical lymphocytes appear on CBC differential. Diagnosis: heterophile antibody test (Monospot) is the rapid screening test — but may be negative in the first 1–2 weeks of illness, especially in young children. EBV-specific antibodies (VCA IgM, VCA IgG, EBNA) provide definitive diagnosis when Monospot is negative. Routine treatment is supportive: rest, adequate hydration, acetaminophen or ibuprofen for fever and pain. Corticosteroids are reserved for severe tonsillar hypertrophy with airway compromise or other severe complications. The critical medication safety point: do NOT administer ampicillin or amoxicillin to patients with mononucleosis — aminopenicillins commonly cause a diffuse maculopapular rash in EBV infection. This is NOT a true penicillin allergy but a specific drug-virus interaction. Document it accurately as 'ampicillin rash with EBV' — not as penicillin allergy. The most important nursing teaching: avoid contact sports and strenuous physical activity for a minimum of 3–4 weeks (some guidelines extend to 8 weeks) due to risk of splenic rupture. The spleen is enlarged and fragile; blunt abdominal trauma can cause life-threatening hemorrhage. Assess for airway compromise from tonsillar hypertrophy. Other complications include hepatitis (elevated liver enzymes — avoid hepatotoxic medications and alcohol), rarely Guillain-Barré syndrome, and very rarely splenic rupture without trauma.

Key Distinctions

The ampicillin/amoxicillin rash in mono is NOT a penicillin allergy — document correctly to avoid lifelong mislabeling. Students frequently select 'antibiotic allergy' as the cause of the rash; the correct answer is the drug-virus interaction specific to EBV. The spleen precaution duration (minimum 3–4 weeks, no contact sports) is the #1 tested nursing point. Do not confuse mono pharyngitis (exudative, with posterior cervical lymphadenopathy and fatigue) with strep pharyngitis (exudative, with anterior cervical lymphadenopathy, no significant fatigue) — rapid strep and Monospot differentiate them.

Clinical Pearl

Amoxicillin + mono = rash. It's not an allergy — label it wrong and the patient loses penicillin forever.