Merck Manual

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Larry M. Bush

, MD, FACP, Charles E. Schmidt College of Medicine, Florida Atlantic University;

Maria T. Vazquez-Pertejo

, MD, FACP, Wellington Regional Medical Center

Reviewed/Revised Mar 2023
Topic Resources

Nocardiosis is an acute or chronic, often disseminated, suppurative or granulomatous infection caused by various aerobic soil saprophytes of the gram-positive bacilli genus Nocardia. Pneumonia is typical, but skin and central nervous system 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. The genus Nocardia has many species and an increasing number are recognized as causes of human disease.

N. asteroides 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 species 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.

Nocardia is found in standing water, decaying plants, and soil. Infection is via inhalation of dust that contains the bacteria or by direct inoculation of the skin when contaminated soil or water enters through a cut or scrape.

Risk factors

Predisposing risk factors for nocardiosis include

  • Lymphoreticular cancers

  • Organ transplantation

  • High-dose corticosteroid or other immunosuppressive therapy

  • Underlying pulmonary disease

However, about 20 to 30% of patients with nocardiosis have no identified preexisting disease or condition. Primary cutaneous nocardiosis usually occurs in immunocompetent patients 1 to 3 weeks after some type of local trauma.

Nocardiosis is also an opportunistic infection in patients with advanced HIV infection.

Symptoms and Signs of Nocardiosis

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 tuberculosis 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

  • Lymphocutaneous syndrome

  • An actinomycetoma

The lymphocutaneous syndrome consists of a primary pyoderma lesion and lymphatic nodules resembling sporotrichosis.

An actinomycetoma due to nocardiosis begins as a nodule, suppurates, spreads along fascial planes, and drains through chronic fistulas.

Diagnosis of Nocardiosis

  • Microscopic examination or culture

Diagnosis of nocardiosis is by identification of Nocardia species 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.

Treatment of Nocardiosis

  • Trimethoprim/sulfamethoxazole (TMP/SMX)

TMP/SMX 15 mg/kg/day (of the TMP component) orally every 6 to 12 hours or high doses of a sulfonamide alone (eg, sulfadiazine 1 g orally every 4 to 6 hours) are used. Because most cases respond slowly, a dose that maintains a sulfonamide blood concentration of 12 to 15 mg/dL 2 hours after the last dose must be continued for a prolonged duration. The duration depends on the type of infection and predisposing risk factors of the infected patient. In immunocompromised patients and patients with disseminated disease, TMP/SMX should be used with amikacin, imipenem, or meropenem pending species identification and susceptibility testing results.

When sulfonamide hypersensitivity or refractory infection is present, amikacin, a tetracycline (particularly minocycline), imipenem/cilastatin, meropenem, ceftriaxone, cefotaxime, extended-spectrum fluoroquinolones (eg, moxifloxacin), or dapsone can be used. Tigecycline may be an effective alternative. In vitro susceptibility data should guide the choice of alternative antibiotics.

Localized abscesses typically require incision, drainage, and surgical debridement.

Prognosis for Nocardiosis

Without treatment, pulmonary nocardiosis and disseminated nocardiosis are usually fatal.

Among patients who are treated with appropriate antibiotics, the case fatality 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%.

Key Points

  • Immunosuppression and chronic pulmonary disease are predisposing factors, but up to 30% of patients have no preexisting disease.

  • Pneumonia is typical, but skin and central nervous system infections are common; hematogenous spread can involve almost any organ.

  • Treat with trimethoprim/sulfamethoxazole (or one of the numerous alternatives) for a prolonged duration.

Drugs Mentioned In This Article

Drug Name Select Trade
Primsol, Proloprim, TRIMPEX
No brand name available
Amikin, Amikin Pediatric, ARIKAYCE
Emtet-500, Panmycin, Sumycin
Amzeeq, Arestin, Dynacin, Minocin, minolira, Myrac, Solodyn, Ximino, Zilxi
Primaxin, Primaxin IM
Ceftrisol Plus, Rocephin
Avelox, Avelox ABC Pack, Avelox I.V., MOXEZA, Vigamox
NOTE: This is the Professional Version. CONSUMERS: View Consumer Version
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