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Clinical Features

Overall, 80% of nocardiosis cases present as invasive pulmonary infection, disseminated infection, or brain abscess; 20% present as cellulitis.

Pulmonary infection commonly presents with fever, cough, or chest pain. It can also present as pneumonia, lung abscesses, or cavitary lesions. Central nervous system (CNS) symptoms include:

  • Headache
  • Lethargy
  • Confusion
  • Seizures
  • Sudden onset of neurologic deficit

Contiguous spread within the thoracic cavity and hematogenous dissemination, particularly to the CNS, are common.

Although incidence data are extremely limited, the number of cases is likely rising as a result of the increase in the number of severely immunocompromised persons. Approxmiately 10% of cases with uncomplicated pneumonia are fatal.

The case-fatality rate increases with overwhelming infection, disseminated disease, or brain abscess. Surgical drainage may be indicated and may improve patient outcome.

Etiologic Agent

photomicrograph tissue sample image from a patient ill with nocardiosis

This hematoxylin-eosin (H&E) stained photomicrograph of a tissue sample of a mycetoma excised from a patient’s thorax ill with nocardiosis, revealed the presence of a tissue granule due to the bacterium, Nocardia brasiliensis.

The majority of cases are caused by Nocardia asteroides complex (at least 50% of invasive infections). The N. asteroides complex is comprised of:

  • N. abscessus
  • N. cyriacigeorgica
  • N. farcinica
  • N. nova

Other known pathogenic species of Nocardia include:

  • N. transvalensis complex
  • N. brasiliensis
  • N. pseudobrasiliensis

Laboratory Diagnostics

In the clinical laboratory, routine cultures may be held for insufficient time to grow Nocardia, and referral to a reference laboratory may be needed for species identification.

N. farcinica is more often resistant to antimicrobial agents, including trimethoprim-sulfamethoxazole (TMP-SMX), and has been shown to be more virulent in an animal model.

TMP-SMX therapy for HIV-infected patients may be complicated by frequent occurrence of side effects and drug resistance. For information on lab submissions, see Special Bacteriology Reference Laboratory (SBRL).

 

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