Rhodococcus equi Infection Differential Diagnoses

Updated: Dec 03, 2018
  • Author: Indira Kedlaya, MD; Chief Editor: Thomas E Herchline, MD  more...
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Diagnostic Considerations

The differential diagnoses for R equi infections include infections with Mycobacterium tuberculosis, other nontuberculous mycobacteria, Nocardia species, fungi, and diphtheroids.

Because of the variable acid-fast nature of R equi infection and its similarity to pulmonary tuberculosis, patients initially being treated for tuberculosis have been reported.

These coccobacilli may be arranged at right angles to each other, leading to confusion with diphtheroids. In patients with cavitary pneumonia, the sputum finding of diphtheroids and other normal commensals should raise suspicion of R equi as the etiologic agent.

The acid-fast nature and the production of aerial hyphae in certain media may lead to a misdiagnosis of Nocardia infection.

R equi can initially cause an interstitial pneumonia. Therefore, an initial diagnosis of Pneumocystis jiroveci pneumonia has been made in patients infected with HIV who have pneumonia .

R equi cavitary pneumonia in a patient infected with HIV or in a patient with neutropenia may be mistaken for fungal pneumonia.

Other noninfectious conditions that may initially be included in the differential diagnoses include lung nodules caused by metastasis and Wegener granulomatosis.

Differential Diagnoses