Rhodococcus equi--an easily missed opportunistic pathogen.

Over the last 10 years Rhodococcus equi has been identified as an important, albeit very rare, opportunistic pathogen. As the number of patients immunocompromised from HIV infection grows, this microorganism will likely become of increasing clinical importance. Infection with R. equi is usually insidious, causing progressive pulmonary disease that is typically pleural based at the time of microbiological diagnosis. As in the case we present, the clinical and microbiological diagnoses may be significantly delayed, either by the common pitfalls encountered in the laboratory identification of R. equi, or by the failure to recognize the pathogenic potential of the isolate. R. equi infection should be suspected in immunocompromised patients with pneumonia, when a pure or predominant growth of aerobic, non-sporeforming gram-positive bacilli is found on cultures of bronchoalveolar lavage fluid and other pulmonary pathogens have been excluded.