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NOCARDIOSIS

Microbiology

Nocardiae are branching, beaded, gram-positive filaments that usually give positive results with modified acid-fast stains. These saprophytic aerobic actinomycetes are common in soil.

  • Nine species or species complexes are most commonly associated with human disease.

  • Speciation of nocardiae is precluded in most clinical laboratories because it is nearly impossible without molecular phylogenetic techniques.

  • Nocardia brasiliensis is most often associated with localized skin lesions.

Epidemiology

Nocardiosis occurs worldwide and has an incidence of ∼0.375 cases per 100,000 persons in Western countries. The risk of disease is greater than usual among persons who have deficient cell-mediated immunity—e.g., that associated with lymphoma, transplantation, glucocorticoid therapy, or HIV infection with <250 CD4+ T cells/μL.

Pathogenesis

Pneumonia and disseminated disease follow inhalation of fragmented bacterial mycelia.

  • Nocardiosis causes abscesses with neutrophilic infiltration and necrosis.

  • Organisms have multiple mechanisms for surviving within phagocytes.

Clinical Manifestations

  • Respiratory tract disease: Pneumonia is usually subacute, presenting over days to weeks, but can be acute in immunocompromised pts.

    • – A prominent cough productive of small amounts of thick purulent sputum, fever, anorexia, weight loss, and malaise are common; dyspnea, hemoptysis, and pleuritic chest pain are less common.

    • – CXR may demonstrate single or multiple nodular infiltrates of varying sizes that tend to cavitate. Empyema is noted in one-quarter of cases.

    • – Extrapulmonary disease is documented in >50% of cases.

  • Extrapulmonary disease: In 20% of cases of disseminated disease, lung disease is absent.

    • – Nocardial dissemination manifests as subacute abscesses in brain (most commonly), skin, kidneys, bone, and/or muscle.

    • – Brain abscesses are usually supratentorial, are often multiloculated, can be single or multiple, and tend to burrow into ventricles or extend into the subarachnoid space.

    • – Meningitis is uncommon, and nocardiae are difficult to recover from CSF.

  • Disease following transcutaneous inoculation: usually presents as cellulitis, lymphocutaneous disease, or actinomycetoma

    • Cellulitis presents 1–3 weeks after a break in the skin (often with contamination by soil).

      • The firm, tender, erythematous, warm, and nonfluctuant lesions may involve underlying structures, but dissemination is rare.

      • N. brasiliensis and species in the N. otitidiscaviarum complex are most common in cellulitis.

    • Lymphocutaneous disease resembles sporotrichosis and presents as a pyodermatous nodule at the inoculation site, with central ulceration and purulent or honey-colored discharge.

      • Subcutaneous nodules often appear along lymphatics that drain the primary lesion.

    • Actinomycetoma progresses from a nodular swelling at the site of local trauma (typically on the feet or hands, although other sites can be affected) to fistula formation; dissemination is rare.

      • The discharge is serous or purulent and can contain granules consisting of masses of mycelia.

      • Lesions, which spread slowly along fascial planes to involve adjacent skin and SC tissue and bone, can cause extensive deformity after months or years.

  • Eye disease: Endophthalmitis can occur after eye surgery or during disseminated disease.

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