Table of contents
Nocardiosis
Background
Overview
Definition
Nocardiosis is an opportunistic infection caused by Nocardia species, aerobic actinomycetes found in soil and decaying organic matter, that primarily affects individuals with immunocompromise.
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Pathophysiology
Nocardia species are Gram-positive, partially acid-fast, lysozyme-resistant, catalase-positive aerobic actinomycetes transmitted via inhalation or direction inoculation. The bacteria can evade immune defenses due to their ability to survive within macrophages, leading to chronic infections.
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Epidemiology
Nocardiosis is more common in tropical and subtropical climates and may also occur more frequently in dry, windy regions, such as the southwestern US. The reported incidence of Nocardia infection among solid organ transplant recipients is 2.65%.
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Risk factors
The most significant risk factor for nocardiosis is immunocompromise, particularly compromised cell-mediated immunity, as seen in HIV infection, solid organ transplantation, allogeneic HSCT, hematologic malignancies, prolonged corticosteroid use, and immunosuppressive therapy. Other risk factors include chronic pulmonary disease, alcohol use disorder, diabetes, and trauma for primary cutaneous infection.
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Disease course
Nocardiosis typically presents as a chronic infection, with symptoms varying based on the affected organs. The lungs are most commonly involved, but the infection can disseminate to other sites, including skin and soft tissues and the CNS. Pulmonary nocardiosis presents with nonspecific respiratory and constitutional symptoms. CNS involvement includes brain abscesses and meningitis, presenting with nonspecific generalized symptoms and focal neurological deficits. Secondary cutaneous infections may develop from lymphatic or hematogenous spread, presenting as painful erythematous subcutaneous nodules with ulcerated draining lesions (sporotrichoid nocardiosis) or larger painless masses (actinomycetoma). Primary cutaneous infection can also occur through direct inoculation.
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Prognosis and risk of recurrence
In the US, the reported 90-day mortality rate is 17.5%.
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Guidelines
Key sources
The following summarized guidelines for the evaluation and management of nocardiosis are prepared by our editorial team based on guidelines from the American Society of Transplantation (AST 2019) and the Infectious Diseases Society of America (IDSA 2014).
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Screening and diagnosis
Diagnostic investigations
Clinical assessment: as per IDSA 2014 guidelines, consider obtaining immediate consultation with a dermatologist familiar with cutaneous manifestations of infection in patients with cellular immune defects (such as patients with lymphoma, lymphocytic leukemia, recipients of organ transplants, or receiving immunosuppressive drugs such as anti-TNF therapy or certain monoclonal antibodies).
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Laboratory testing
Brain imaging
Diagnostic procedures
Medical management
Management of nonsevere disease
As per AST 2019 guidelines:
Administer TMP/SMX as first-line therapy for Nocardia infections. Consider administering monotherapy for localized skin infection or stable patients with pneumonia.
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Administer imipenem, ceftriaxone, or linezolid as first-line options for Nocardia infections in patients with sulfa allergy.
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Management of severe disease
Duration of therapy
Surgical interventions
Preventative measures
Secondary prophylaxis
As per AST 2019 guidelines:
Consider initiating TMP/SMX to prevent primary Nocardia infection or relapse after treatment, although infections can occur despite prophylaxis. Consider prescribing one double-strength tablet daily (dose-adjusted for renal function) for secondary prophylaxis after an episode of nocardiosis.
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Recognize that non-TMP/SMX antimicrobials used as alternatives for Pneumocystis jiroveci prophylaxis may provide inadequate protection against nocardiosis.
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