CRT & RRT Exam Secrets Study Guide

"How to Ace the Certified Respiratory Therapist (CRT) Exam and Registered Respiratory Therapist (RRT) Exam, using our easy step-by-step CRT & RRT test study guide, without weeks and months of endless studying..." Morrison Media

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.

Several Nocardia sp, in the family Actinomycetaceae, cause human disease. The most common human pathogen is N. asteroides, which 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. Nocardiosis occurs worldwide in all age groups, but incidence is greater among older adults, especially men. Person-to-person spread is rare. Lymphoreticular malignancies, organ transplantation, high-dose corticosteroid or other immunosuppressive therapy, and underlying pulmonary disease are predisposing factors, but about 1⁄2 the patients have no preexisting disease. Nocardiosis is also an opportunistic infection in patients with advanced HIV infection. Other Nocardia sp sometimes cause localized or, occasionally, systemic infections.

Symptoms and Signs

Nocardiosis usually begins as a subacute pulmonary infection that resembles actinomycosis, but Nocardia is more likely to disseminate locally or hematogenously. Dissemination with abscess formation may involve any organ but most commonly affects the brain, skin, kidney, 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 also may occur. Metastatic brain abscesses, occurring in 30 to 50% of cases, usually produce 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 a 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

Diagnosis is by identification of Nocardia sp in tissue or culture 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. Nocardia do not develop a clubbed appearance, as does Actinomyces israelii.

Prognosis and Treatment

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 lowest (about 10%) in immunocompetent patients with lesions restricted to the lungs. Cure rates for patients with skin infection are usually > 95%.

Trimethoprim-sulfamethoxazole or high doses of a sulfonamide alone (sulfamethoxazole or sulfisoxazole) are used. Because most cases respond slowly, a dose that maintains a sulfonamide blood concentration of 12 to 15 mg/dL (eg, with sulfadiazine 4 to 6 g/day po) must be continued for several months. When sulfonamide hypersensitivity or refractory infection is present, amikacin, a tetracycline (particularly minocycline), imipenem-cilastatin, ceftriaxone, cefotaxime, or cycloserine can be used. In vitro susceptibility data should guide the choice of alternative drugs.

Last full review/revision November 2005

Home | Shop | Contact Us | About Us