A. Organism

1. Aerobic Gram positive rod-shaped bacterium, forms branching chains
2. Found in soil
3. N. asteroides causes ~85% of human infections
4. N. brasiliensis, N. farcinia, N. nova, N. transvalensis less common
5. Morphology similar to actinomyces
6. About 2/3 of cases in patients with (severely) impaired cell-mediated immunity
7. Uncommon infection in USA, 500-1000 cases per year

B. Infection

1. Pulmonary infection is most common
   1. Usually begins with inhalation of organism from dust or soil
   2. Main pulmonary pathogen is N. asteroides
   3. Lung abscesses may form, with large amounts of pus
   4. Most common complication of pulmonary disease is dissemination to brain
2. Soft Tissue Infections (very rare) [2]
   1. Usually caused by N. brasiliensis
   2. Contracted by skin puncture
   3. Lymphangitis, often nodular, may occur
   4. Painful, purulent, nodules and fever are typically seen
3. Renal, pericardial and other disseminated disease is possible

C. Clinical Presentation [3]

1. About 2/3 of patients with nocardiosis have impaired cell-mediated immunity
   1. Diabetes Mellitus
   2. Organ Transplantation
   3. Lymphoma or other solid tumors
   4. Immunosuppression with glucocorticoids and cytotoxic agents [4]
   5. Pulmonary Alveolar Proteinosis is also a risk factor
2. About 1/3 of patients with nocardiosis are immunocompetent
3. Fever, thick sputum production usually occur after consolidated pneumonia develops
4. Focal Central Nervous System (CNS) with pneumonia is classic for Nocardia infection
5. Chest Radiography may show consolidated pneumonia

D. Diagnosis

1. Must be considered in differential diagnosis of patients with immunosuppression
2. May be seen on gram stain if sputum or bronchealveolar lavage sample is good
3. Cultured if laboratory directed to search for the organism (grows slowly)

E. Treatment [1]

1. Generally prolonged course required, at least 6 months is recommended
2. Very sensitive to sulfonamides such as TMP/SMX (Bactrim®/Septra®) 1 DS po bid
3. Minocycline is also effective
4. In difficult cases, imipenem and/or amikacin have been used
5. Linozolid is also active
6. In vitro sensitivity testing is not standardized
7. Therefore, clinical response must be used to direct changes in therapy
8. Changes in erythrocyte sedimentation rate (ESR) may be useful to follow response

References

1. Safdar N, Kaul DR, Saint S. 2007. NEJM. 356(9):943 (Case Discussion)
2. Slevogt H, Schiller R, Wesselmann H, Surttorp N. 2001. Lancet. 357(9258):768 (Case Report)
3. Freedman AS and Nielsen GP. 1999. NEJM. 340(15):1188 (Case Record)
4. Drapkin MS and Mark EJ. 2000. NEJM. 343(12):870 (Case Record)