Workup
Laboratory Studies
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Gram staining is indicated in nocardiosis.
- Directly examine clinical materials (eg, sputum, bronchoalveolar lavage, cerebral spinal fluid, pus) by Gram stains and acid-fast stains (modified Ziehl-Neelsen stains). Delicately branched, weakly gram-positive, variably acid-fast bacilli with tendency to fragment are indicative of Nocardia.
- Use methenamine-silver stains for demonstrating the organisms in tissue specimens.
- Inoculate clinical material, including blood specimens, on brain-heart infusion media or Sabouraud agar without antibiotics. N asteroides and N braziliensis are obligate aerobes, thermophilic, and slow growing. Colonies take 1-2 weeks to develop and are usually waxy then chalky in appearance.
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Serological diagnosis is not readily available.
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Cultures typically grow within 3-5 days on blood or chocolate agar, but cultures from normally sterile sites should be maintained for 3 weeks in a liquid medium.
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Case reports of positive testing for beta-D-glucan with nocardial infections have been published, [8, 9] but it isn't always clear whether concomitant infection with a fungus or Pneumocystis was ruled out. In some cases PCP or a candidal infection were discovered shortly after the Nocardia diagnosis, both of which would produce elevated beta-D-glucan levels.
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Imaging Studies
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Generalized infections
- Chest radiographic findings vary and include fluffy infiltrates, scattered nodules, and confluent lobar infiltrates progressing to complete consolidation and cavitation.
- Chest CT scanning may be necessary to visualize the extent of disease and to rule out empyema.
- CT scanning with contrast or MRI may be necessary to visualize cerebral abscesses.
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Disseminated nocardiosis
- Perform CT scanning with contrast or MRI to rule out cerebral abscesses. Because of the high incidence of spread to the brain, all patients with pulmonary nocardiosis should have a neuroimaging study, even in the absence of CNS symptoms. Lesions should show ring-enhancement with contrast and fluid-attenuated inversion recovery (FLAIR). Early lesions, or those present during treatment with steroids, may not enhance and may mimic infarction.
- Use 2-dimensional echocardiography to rule out vegetations.
- Perform abdominal and/or pelvic sonography and CT scanning to rule out intra-abdominal, hepatic, splenic, or renal abscesses.
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Procedures
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A bronchoalveolar lavage is recommended in immunocompromised individuals in whom nocardiosis is suspected because mortality can exceed 50% without rapid diagnosis and treatment.
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