These organisms are Gram positive, partially acid-fast, and true branching filamentous bacteria. They may produce either localized skin infections or disseminated involvement. Nocardiosis usually follows an indolent course of one to three weeks before being recognized, but immunocompromised patients may suffer rapid progression of disease within days. 6 Primary cutaneous disease typically follows traumatic implantation of Nocardia brasiliensis into subcutaneous tissue, although all Nocardia sp can cause cutaneous disease. 4,8 Primary cutaneous Nocardia infections first appear as small, firm, painless subcutaneous nodules.
Sinus tracts develop as the lesion grows.
Granules are absent in the sinus discharge of Nocardia brasiliensis lesions, distinguishing them from other causes of mycetoma. Cutaneous foci may spread along fascial planes or lymphatics or occasionally via the blood. The disease may invade bone, blood vessels, and lymphatic vessels, paving the way for secondary bacterial infections at any of these sites. The incidence of nocardiosis in the United States is estimated to be 500 to 1,000 cases each year. The preponderance of Nocardia brasiliensis cases arise in the Southern and Southwestern United States.