Overall, 80% of cases present as invasive pulmonary infection, disseminated disease, or brain abscess; 20% present as cellulitis. For pulmonary diseases common symptoms are fever, cough, and chest pain; for central nervous system disease symptoms are usually headache, lethargy, confusion, seizures, and sudden onset of neurologic deficit.

Causes

Nocardia asteroides (causes at least 50% of invasive infections). Other pathogenic species include N. farcinica, N. nova, N.transvalensis, N. brasiliensis, and N. pseudobrasiliensis. In the United States, an estimated 500-1,000 new cases of Nocardia infection occur annually. An estimated 10%-15% of these patients also have HIV infection.

Risk Factors

Pulmonary and disseminated infections occur through inhalation and primary cutaneous disease through soil-contaminated wounds. Rarely, nosocomial postsurgical transmission occurs. Approximately 10% of cases with uncomplicated pneumonia are fatal. Case-fatality rate increases with overwhelming infection, disseminated disease, or brain abscess. Surgical drainage may be indicated and may improve patient outcome. Severely immunocompromised persons (e.g., persons with malignancy, connective tissue disorders, bone marrow or solid organ transplantation, high-dose corticosteroid use, or HIV infection), alcoholism or pulmonary alveolar proteinosis, and males (ratio male:female = 3:1)

Diagnosis

Diagnosis may be difficult. In the clinical laboratory, routine cultures may be held for insufficient time to grow nocardiae, and referral to a reference laboratory may be needed for species identification. Recently, N. farcinica and N. nova have been removed from N.asteroides complex. N. farcinica frequently is more resistant to antimicrobial agents, including trimethoprim-sulfamethoxazole (TMP-SMX) (the drug of choice), 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.

Treatment

A new combination drug therapy (sulfonamide, ceftriaxone, and amikacin) has shown promise for infections difficult to treat. Application of newer molecular diagnostic and subtyping methods may assist in earlier diagnosis and outbreak investigation. In 1998 MSPB described a rapid PCR-based method to differentiate N. farcinica from other nocardiae.

References

CDC