Diagnostic dilemma: Epstein-Barr virus (EBV) infectious mononucleosis with lung involvement or co-infection with Legionnaire's disease?

BACKGROUND: Hospitalized adults with fever and "pneumonia" can be a difficult diagnostic challenge particularly when the clinical findings may be due to different infectious diseases. METHODS: We recently had an elderly female who presented with fever, fatigue and dry cough with elevated serum transaminases and lung infiltrates. The diagnosis of Epstein-Barr virus (EBV) infectious mononucleosis (IM) was made based on a positive Monospot test, elevated EBV VCA IgM titer, and highly elevated EBV viral load. Her chest infiltrates were not accompanied by hilar adenopathy which may occur with EBV IM. Her dry cough persisted and she developed abdominal pain. RESULTS: Legionnaire's disease was considered because she had extra-pulmonary findings characteristic of Legionnaire's disease, e.g., relative bradycardia, abdominal pain, hyponatremia, hypophosphatemia, elevated ferritin levels, microscopic hematuria. Legionella titers were negative, but Legionella (serogroup 1) urinary antigen was positive. CONCLUSIONS: We present a diagnostic dilemma in an elderly female with both Legionnaire's disease and Epstein-Barr virus infectious mononucleosis with pulmonary involvement.