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, [9, 10] 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.
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. [11, 12]
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.
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.
