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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.
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Nine species or species complexes are most commonly associated with human disease.
Speciation of nocardiae is precluded in most clinical laboratories, although improvements in mass spectrometry–based techniques may change this limitation in high-resource countries.
Nocardia brasiliensis is most often associated with localized skin lesions.
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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, HIV infection with <250 CD4+ T cells/µL, or immunomodulating drugs such as tumor necrosis factor inhibitors.
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Pneumonia and disseminated disease follow inhalation of fragmented bacterial mycelia.
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CLINICAL MANIFESTATIONS
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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 the brain (most commonly), skin, kidney, bone, eye, 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.
– 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 ...