Rhodococcus equi infection in transplant recipients: a case of mistaken identity and review of the literature.

The incidence of Rhodococcus equi infection in solid-organ transplant recipients continues to rise throughout the world. Unfortunately, this opportunistic pathogen is still underestimated and potentially disregarded by physicians and microbiology laboratories due to its morphology on Gram staining. Pulmonary involvement is the most common finding in the immunocompromised host. We report a case of a 63-year-old heart-transplant recipient who presented with increasing fatigue and nonproductive cough for 3 weeks. After full evaluation, a lung abscess was demonstrated by thoracic computerized tomography (CT). Blood and sputum cultures were remarkable for heavy "diphtheroids." Although the Gram-stain result was initially interpreted as a contaminant, a clinical suspicion for Rhodococcus assisted in further investigation. Broncheoalveolar lavage and CT-guided biopsy of the lung abscess revealed heavy growth of diphtheroids. However, further evaluation by a reference laboratory demonstrated mycolic acid staining consistent with R. equi. Surgical drainage and prolonged antibiotic therapy resulted in complete remission of the pneumonia and abscess. This represents the fourth reported case of R. equi infection in a heart transplant recipient. It is imperative that all physicians and laboratory staff consider R. equi when an immunocompromised patient has any type of pneumonia, especially with abscess formation.