When Infections Co-exist: Infectious Mono and Diphtheria

Infectious mononucleosis was tentatively diagnosed in a patient who presented with a temperature of 39.5°C, red throat and enlarged nodes in the neck. He was given amoxycillin 250 mg tid and was admitted to hospital, where his clinical symptoms of diphtheria were investigated. Medication was switched to penicillin V 300 mg tid. On the fifth hospital day the laboratory reported a culture of a toxigenic strain of C. diphtheriae from an initial throat swab.On the same day, he developed an erythematous, highly pruritic maculopapular rash which was probably caused by the initial use of amoxycillin. The rash initially became generalized and slowly resolved in 7-9 days. He apparently had infectious mononucleosis and a coincidental pharyngeal infection with toxigenic C. diphtheriae.No indication exists for the use of antibiotics in infectious mononucleosis, unless throat cultures reveal bacterial pathogens. In that case, an appropriate antibiotic other than ampicillin-amoxycillin can be chosen.