Nocardiosis is an acute or chronic, often disseminated, suppurative or granulomatous infection caused by various aerobic soil saprophytes of the genus Nocardia. Pneumonia is typical, but skin and CNS infections are common. Diagnosis is by culture and special stains. Treatment is usually with sulfonamides.
Nocardia are obligate aerobic, partially acid-fast, beaded, branching, gram-positive bacilli. Several Nocardia sp, in the family Actinomycetaceae, cause human disease.
N. asteroides is the most common human pathogen; it usually causes pulmonary and disseminated infection.
N. brasiliensis most commonly causes skin infection, particularly in tropical climates. Infection is via inhalation or by direct inoculation of the skin.
Other Nocardia sp sometimes cause localized or, occasionally, systemic infections.
Nocardiosis occurs worldwide in all age groups, but incidence is higher in older adults, especially men, and immunocompromised patients. Person-to-person spread is rare.
Lymphoreticular cancers, organ transplantation, high-dose corticosteroid or other immunosuppressive therapy, and underlying pulmonary disease are predisposing factors, but about one half of patients have no preexisting disease. Nocardiosis is also an opportunistic infection in patients with advanced HIV infection.
Symptoms and Signs
Nocardiosis usually begins as a subacute pulmonary infection that resembles actinomycosis, but Nocardia are more likely to disseminate locally or hematogenously. Dissemination with abscess formation may involve any organ but most commonly affects the brain, skin, kidneys, bone, or muscle.
The most common symptoms of pulmonary involvement—cough, fever, chills, chest pain, weakness, anorexia, and weight loss—are nonspecific and may resemble those of TB or suppurative pneumonia. Pleural effusion may also occur. Metastatic brain abscesses, occurring in 30 to 50% of cases, usually cause severe headaches and focal neurologic abnormalities. Infection may be acute, subacute, or chronic.
Skin or subcutaneous abscesses occur frequently, sometimes as a primary local inoculation. They may appear as firm cellulitis, a lymphocutaneous syndrome, or an actinomycetoma. The lymphocutaneous syndrome consists of a primary pyoderma lesion and lymphatic nodules resembling sporotrichosis. An actinomycetoma begins as a nodule, suppurates, spreads along fascial planes, and drains through chronic fistulas.
Diagnosis is by identification of Nocardia sp in tissue or in culture of samples from localized lesions identified by physical examination, x-ray, or other imaging studies. Clumps of beaded, branching filaments of gram-positive bacteria (which may be weakly acid-fast) are often seen.
Without treatment, pulmonary and disseminated nocardiosis are usually fatal. Among patients who are treated with appropriate antibiotics, the mortality rate is highest (> 50%) in immunocompromised patients with disseminated infections and is about 10% in immunocompetent patients with lesions restricted to the lungs. Cure rates for patients with skin infection are usually > 95%.
TMP/SMX 15 mg/kg/day (of the TMP component) po q 6 to 12 h or high doses of a sulfonamide alone (eg, sulfadiazine 1 g po q 4 to 6 h) are used. Because most cases respond slowly, a dose that maintains a sulfonamide blood concentration of 12 to 15 mg/dL 2 h after the last dose must be continued for ≥ 6 mo.
When sulfonamide hypersensitivity or refractory infection is present, amikacin, a tetracycline (particularly minocycline), imipenem/cilastatin, meropenem, ceftriaxone, cefotaxime, extended-spectrum fluoroquinolones (eg, moxifloxacin), dapsone, or cycloserine can be used. Linezolid and tigecycline may be effective alternatives. In vitro susceptibility data should guide the choice of alternative drugs.
Last full review/revision April 2013 by Larry M. Bush, MD; Maria T. Perez, MD