Rhodococcus Equi

Epidemiology

  • Predisposing Factors:
    • Impaired Cell-Mediated Immunity:
      • Steroids
      • HIV
      • Solid Organ Transplantation
    • Animal Exposure: reported in most, but not all, patients

Etiology

  • Rhodococcus equi infection
  • Gram-Positive Coccus or Rod: may stain weakly acid-fast (due to mycolic acid in cell wall), but is much smaller than AFB
    • Varies in shape from cocci to curved club shape (frequently misinterpreted as a diphtheroid or bacillus)

Physiology

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Diagnosis

  • Sputum GS/Cult+Sens:
    • Gram-Positive Coccus or Rod: may stain weakly acid-fast (due to mycolic acid in cell wall), but is much smaller than AFB
      • Varies in shape from cocci to curved club shape (frequently misinterpreted as a diphtheroid or bacillus)
  • FOB:
  • CXR/Chest CT Pattern:
    • Nodular Infiltrates: gradually cavitate
    • Lung Abscess:
    • Empyema: may occur

Clinical

  • Subacute Onset of Disease (resembling fungal or mycobacterial disease):

Treatment

  • Vanco or Erythromycin: agents of choice (as Rhodococcus is intracellular and these agents get into cells readily)
    • Addition of Rifampin: may be synergistic
    • Prolonged therapy is necessary to prevent relapse
  • Alternatives: resistance has been reported to occur while receiving ß-lactams
    • Rifampin:
    • Chloramphenicol:

References

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