Streptococcus equinus endocarditis in a patient with pulmonary histiocytosis X

Although Streptococcus equinus has been isolated from the human bowel in an appreciable percentage of the adult general population, it has only rarely been described as a human pathogen. Our report describes the occurrence of S. equinus endocarditis in a patient who had no history of pre-existing heart disease, but who showed evidence of a late-stage pulmonary histiocytosis X. Endocarditis resolved promptly after antibiotic treatment, but required aortic valve substitution. Abnormalities of the immune system that have been demonstrated in patients with histiocytosis X could explain the occurrence of endocarditis in this patient.