Opportunistic lung infection caused by Rhodococcus (Corynebacterium) equi.

Rhodococcus (formerly Corynebacterium) equi, a common animal pathogen, can cause a slowly evolving pneumonia in humans, particularly immunocompromised people. The authors describe two patients; one with acquired immunodeficiency syndrome. On chest radiographs, R. equi produces chronic, localized pulmonary opacities that can cavitate. The main differential diagnoses are tuberculosis and fungal infection.