Rhodococcus equi Clinical Presentation

Updated: Apr 13, 2015
  • Author: Indira Kedlaya, MD; Chief Editor: Burke A Cunha, MD  more...
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Presentation

History

The onset of R equi infections is generally insidious, and presenting symptoms vary according to the infection site. Symptoms in immunocompetent patients do not differ from those in immunocompromised patients. In R equi infections secondary to trauma, such as endophthalmitis, septic arthritis, and traumatic meningitis, symptoms may present within 24 hours of the trauma.

Pulmonary R equi infections include the following:

  • Fever and cough (>80% of patients with pulmonary R equi infections)
  • Malaise
  • Chest pain
  • Dyspnea
  • Hemoptysis
  • Weight loss
  • Possible chronic or relapsing course
  • Possible community-acquired pneumonia that fails to respond to empirical treatment

Other presentations of R equi infection include lymphadenopathy, eye drainage and pain, joint pain, altered level of consciousness, bloody diarrhea, and fever of unknown origin. Anemia caused by colonic polyps infected with R equi has also been reported. [10]

R equi infections can also be acquired nosocomially. Poststernotomy infection after coronary artery bypass grafting has been reported twice, and postneurosurgical brain abscess has been reported once (although not officially). R equi infection after placement of a ventriculoperitoneal (VP) shunt has also been reported twice.

Epidemiological history is important. Exposure to soil contaminated with manure is the most likely route of both animal and human infection. Exposure is usually inhalational, but infections via the oral route (due to ingestion of soil or food) or via direct inoculation due to trauma have also been well described. A history of animal exposure may be absent.

R equi has been found in bovine, porcine, and equine fecal flora and grows best at summer temperatures. Isolation of the organism from the air on horse farms rises with ambient temperature and is highest on dry windy days.

In addition, a history concerning any preexisting immunocompromising conditions should be obtained. These include malignancy, recent chemotherapy, solid organ or bone marrow transplantation, diabetes mellitus, alcoholism, and immunosuppressive medications. History pertaining to sexual practices and injection drug use is also important.

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Physical

Physical findings depend on the site of infection and include the following:

  • Fever
  • Tachypnea, crackles, and other common physical findings of pneumonia
  • Lymphadenopathy
  • Septic arthritis
  • Corneal laceration, hyperemia, decreased visual acuity, evidence of anterior chamber involvement (eg, hypopyon)
  • Findings of meningitis
  • Soft-tissue masses, induration, fluctuance in localized infections consistent with abscesses, examination of postoperative sites
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Causes

About 80-90% of patients with R equi infection are immunocompromised. About 50-60% of the patients have HIV infection, 15-20% have hematopoietic and other malignancies, and 10% are transplant recipients. Infections have been reported in the following immunocompromised conditions:

  • AIDS: In a study by Capdevila et al (1997) of 78 patients infected with HIV who developed R equi pneumonia, 71 patients met criteria for AIDS and at least 60 of 78 patients had CD4 + counts of less than 200 cells/µL. [9] In another study, by Donisi et al (1996), involving R equi pneumonia in patients infected with HIV, the mean CD4 + count was 47.7 cells/µL. [11]
  • Lymphoma, leukemia, and other malignancies: This includes immunosuppression associated with chemotherapy, such as neutropenia. Neutropenic fever due to R equi bacteremia has been described.
  • Transplantation, including solid organ (kidney, liver, heart) and bone marrow. Renal transplantation is the most frequently associated solid organ transplant. Most cases involved immunosuppressed patients who were receiving a combination of steroids and two of the following: azathioprine, mycophenolate, or a calcineurin inhibitor. [12]
  • Chronic renal insufficiency and patients with end-stage renal disease on peritoneal dialysis
  • Alcoholism
  • Diabetes mellitus
  • Patients receiving immunosuppressive therapy, including corticosteroids

R equi infections can also occur in immunocompetent persons. Infections in these patients include pneumonia, endophthalmitis, septic arthritis, traumatic meningitis, brain abscess, fever of unknown origin, lymphangitis, and lymphadenitis. [13] A history of trauma should be obtained because about 50% of R equi infections described in immunocompetent patients are due to trauma. A recent case report of granulomatous mastitis due to R equi has been reported in an immunocompetent person. [14]

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