Definition of Nocardiosis

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Nocardiosis: An infection with bacteria called Nocardia which tend to strike the lungs, brain and skin, particularly in people with an impaired immune system. The majority (about 80%) of cases of nocardiosis involves lung infection, brain abscess, or disseminated (widespread) disease from Nocardia. The remaining 20% of cases are localized to the skin and cause cellulitis (skin infection).

The most common symptoms with the pulmonary form of nocardiosis are fever, cough, and chest pain. With brain nocardiosis, the symptoms are usually headache, lethargy, confusion, seizures, and sudden onset of neurologic problems.

Nocardia is ubiquitous in the environment. It is in the soil and in dust particles. The inhalation of Nocardia spores usually initiates pulmonary nocardiosis. The skin form of nocardiosis is contracted through soil contamination of wounds. There is no evidence for person-to-person transmission of Nocardia.

Outbreaks of nocardiosis can occur in immunocompromised patients, including persons with malignancy, connective tissue disorders, bone marrow transplantation or solid organ transplantation, high-dose corticosteroid use, and HIV/AIDS.

The diagnosis of Nocardia may be difficult. Newer molecular diagnostic and subtyping methods can assist in earlier diagnosis. Nocardia asteroides is responsible for at least 50% of invasive Nocardia infections. Other species of Nocardia that may cause disease include N. farcinica, N. nova, N.transvalensis, N. brasiliensis, and N. pseudobrasiliensis.

Long-term antibiotic therapy (usually with sulfonamides) may be given for 6 months to a year or longer depending on the individual and site involved. Frequently, chronic suppressive therapy may be needed with prolonged, low-dose antibiotic therapy. In addition, patients with abscesses may need surgery to ensure adequate drainage.

The antimicrobial combination of trimethoprim-sulfamethoxazole (TMP-SMX) is the drug of choice for nocardiosis. However, resistance to TMP-SMX is becoming more common. A new combination drug therapy (sulfonamide, ceftriaxone, and amikacin) has shown promise for infections difficult to treat with TMP-SMX.

About 10% of cases of uncomplicated Nocardia pneumonia are fatal. The fatality rates increase with overwhelming infection, disseminated disease, and brain abscess.