Case reports: pericarditis and lymphadenitis due to Rhodococcus equi.

Most patients with Rhodococcus equi infection are immunocompromised by either HIV infection, malignancy, or medication. Diagnosis is frequently missed or delayed because the organisms, resembling diphtheroids on smears, may be regarded as contaminants. Their clinical, pathologic, histochemical, and microbiologic resemblance to mycobacteria can result in misdiagnosis. Two cases were seen recently in our institution. R. equi pericarditis developed in a 29-year-old woman with failed renal transplant and R. equi axillary lymphadenitis developed in an asymptomatic 27-year-old man. These patients are important because the former is the first reported case of R. equi pericarditis, and the second case was unusual because of the absence of immunocompromise.