NOCARDIOSIS : CLINICAL ASPECTS
Pulmonary infection is usually a confluent bronchopneumonia that may be acute, chronic, or relapsing. Production of cavities and extension to the pleura are common. Symptoms are those of any bronchopneumonia, including cough, dyspnea, and fever. The clinical signs of brain abscess depend on its exact location and size; the neurologic picture can be particularly confusing when multiple lesions are present. The combination of current or recent pneumonia and focal CNS signs is suggestive ofNocardia infection. The cuta-neous syndrome typically involves a pustule, fever, and tender lymphadenitis in the re-gional lymph nodes.
The diagnosis of Nocardia infection is much easier than that of actinomycosis, because the organisms are present in greater numbers throughout the lesions. Filaments of Gram-positive rods with primary and secondary branches can usually be found in sputum and are readily demonstrated in direct aspirates from skin or other purulent sites. Demonstra-tion of acid-fastness, when combined with other observations, is diagnostic of N. aster-oides or N. brasiliensis. The acid-fastness of Nocardia species is not as strong as that ofmycobacteria. The staining method thus employs a decolorizing agent weaker than that used for the classic stain. Culture of Nocardia is not difficult, because the organisms grow on blood agar. It is still important to alert the laboratory to the possibility of nocardiosis, because the slow growth of Nocardia could cause it to be overgrown by the respiratory flora commonly found in sputum specimens. Specific identification can take weeks due the unconventional tests involved.
Nocardia are usually susceptible to sulfonamide, but relatively resistant to penicillin. Thetrimethoprim – sulfamethoxazole combination is the most widely used chemotherapeutic regimen. Technical difficulties in susceptibility testing have hampered the rational selec tion and study of other antimicrobics, but various reports support clinical activity of newerβ-lactams (imipenem, ceftriaxone), minocycline, and aminoglycosides. Antituber-culous agents and antifungal agents such as amphotericin B have no activity against No-cardia.