No Known Risk Factors: approximately 50% of Nocardia cases have no known risk factors
Microbiology
Nocardia Species
Nocardia Asteroides: accounts for 80% of Nocardiosis cases
Nocardia Brasiliensis and Other Species (Nocardia Otitidiscaviarum, Nocardia Nova, Nocardia Farcinica, etc): account for 20% of Nocardiosis cases
Taxonomy
Genus Nocardia is a Member of Family Actinomycetaceae (Colloquially Termed “Actinomycetes”) (see Actinomycetaceae)
All of the Actinomycetes Organisms are Morphologically Similar and Exhibit Characteristic Filamentous Branching with Fragmentation into Bacillary or Coccoid Forms
Origin
Nocardia Exists Ubiquitously in Nature as a Soil Contaminant
Features
Gram-Positive, Beaded, Branching Filamentous Rod
Nocardia Stains Weakly Acid-Fast
Nocardia Requires Aerobic Growth Conditions: in contrast, Actinomyces requires anaerobic growth conditions (see Actinomycosis)
Nocardia Can Be Grown on Standard Culture Medium (Blood Agar or Sabouraud’s): however, growth may not be apparent for 3-21 days
Physiology
Portals of Nocardia Infection
Respiratory Tract
Skin
Gastrointestinal Tract
Local Extension: Nocardia extends from lung to pleural space (with or without chest wall involvement) in 10% of cases
Symptoms May Be Present for Weeks Prior to Presentation
Immunosuppressed Patients May Have Fulminant Presentation
Diagnostic
Sputum Gram Stain/Culture and Sensitivity (see Sputum Culture): although Nocardia frequently colonizes the respiratory tract, culturing the organism from sputum is highly predictive of infection
Has In Vitro Activity Against Most Nocardia Species
Combination Therapy
General Comments
Combination Therapy May Provide Enhanced Activity: recommended as initial therapy with de-escalation to a single agent (as dictated by clinical response)
Imipenem + Cefotaxime
Amikacin + Sulfamethoxazole-Trimethoprim
Imipenem + Sulfamethoxazole-Trimethoprim
Imipenem + Amikacin
Duration of Therapy
Immunocompetent Patients with Isolated Pulmonary or Non-Central Nervous System Multifocal Nocardiosis: 6-12 mo
Immunosuppressed Patients: ≥12 mo
Drainage of Abscesses/Empyema
Required
Prognosis
Mortality Rate: near 50% in those with CNS disease
Mortality Rate: <10% in those with only pulmonary disease
Nocardiosis: updates and clinical overview. Mayo Clin Proc. 2012 Apr;87(4):403-7. doi: 10.1016/j.mayocp.2011.11.016 [MEDLINE]
Current treatment for nocardia infections. Expert Opin Pharmacother. 2013 Dec;14(17):2387-98. doi: 10.1517/14656566.2013.842553. Epub 2013 Oct 4 [MEDLINE]
Experience with linezolid for the treatment of nocardiosis in organ transplant recipients. J Infect. 2015 Jan;70(1):44-51. doi: 10.1016/j.jinf.2014.08.010. Epub 2014 Aug 30 [MEDLINE]