Cold agglutinin disease in a patient with Legionnaires' disease.

We present a case of Legionnaires' disease complicated by cold agglutinin disease. Therapy with erythromycin gluceptate was associated with resolution of both the pneumonia and the hemolysis. Complement-fixing antibody levels to Mycoplasma pneumoniae, influenza A, and adenoviruses were measured repeatedly throughout the clinical illness and were persistently nondiagnostic. The cold agglutinin present in the patient's serum was characterized as an IgM that demonstrated anti-I specificity. Thus, Legionella pneumophila should be considered a potential causative agent in patients with pneumonia and cold agglutinin disease.