Infectious mononucleosis complicated by severe Mycoplasma pneumoniae infection.

A 14-year-old girl with infectious mononucleosis and secondary immunosuppression had severe dyspnea and cough, spiking fever, rales, and diffuse bilateral pulmonary infiltrates. The pulmonary disease progressed rapidly, necessitating empiric trials of antimicrobial agents. Mycoplasma pneumoniae was isolated from a lung biopsy specimen, transtracheal aspirate, and expectorated sputum, but the relatively long period required to isolate the organism delayed the microbiologic diagnosis. Serologic study of acute and convalescent serum samples confirmed the M pneumoniae infection. Clinical improvement was gradual, and the immunosuppression was transient. The patient's illness appeared to represent microbial synergism, with severe M pneumoniae infection complicating transient immunosuppression induced by infectious mononucleosis.