Figure 145.1 Nocardia, Gram stain. (Courtesy of David Schlossberg MD.)
Nocardiosis is typically a suppurative infection with multiple abscesses. It is rarely granulomatous and not fibrotic. Acquisition of infection is by inhalation or by traumatic inoculation. Although nocardia are ubiquitous, they rarely colonize the human respiratory tract. Accordingly, treatment should be initiated when nocardia are isolated repeatedly from pulmonary specimens, particularly in an immunocompromised host. Antimicrobial therapy (alone or in combination with surgical drainage) is recommended, and the duration of therapy must be prolonged to prevent relapse.
More than 75% of patients with systemic nocardiosis possess underlying risk factors. Predisposing conditions are listed in Table 145.1. As the number of solid organ and hematopoietic stem cell transplantations has increased, the incidence of nocardiosis has risen. There is a correlation with the level of immunosuppression following transplantation, with most cases of nocardiosis occurring >1 but <12 months after transplantation, and any time following intensified immunosuppression. Among human immunodeficiency virus (HIV)-infected persons, there is also a correlation with level of immunosuppression, as almost all cases of nocardiosis occur in individuals with CD4 lymphocyte count ≤100 cells/mm3. In both of these severely immunocompromised populations, co-occurrence of other opportunistic infections, particularly aspergillosis, may be found and should be sought if expected clinical improvement fails to occur with therapy.
Chronic pulmonary disease Alcoholism Cirrhosis Lymphoreticular malignancy Diabetes | Solid organ transplantation Hematopoietic stem cell transplantation Chronic corticosteroid use Other drug-induced immunosuppression Cushing syndrome | Systemic lupus erythematosus Systemic vasculitis Ulcerative colitis Sarcoidosis | Renal failure Whipple’s disease Hypogammaglobulinemia Chronic granulomatous disease Human immunodeficiency virus infection Pulmonary alveolar proteinosis |
Nocardiosis remains an uncommon opportunistic complication of HIV infection and transplant recipients. One explanation is that the prophylactic use of trimethoprim–sulfamethoxazole (TMP–SMX), pyrimethamine, or dapsone for Pneumocystis jirovecii (carinii) may also prevent nocardiosis. A minority of HIV-infected persons and transplant recipients diagnosed with nocardiosis had been receiving these drugs prophylactically. The nocardia isolates causing these infections are seldom resistant to sulfa drugs in vitro.
Pathogenesis of systemic nocardiosis
Neutrophils inhibit the growth of nocardia, but eradication of organisms requires cell-mediated immunity. If cellular immunity is impaired, nocardia can cause indolent abscesses with slow spread to distant sites, such as the brain or cerebrospinal fluid. Illness is usually subacute to chronic but may be fulminant in an immunocompromised host. Weight loss, anorexia, and fatigue are common in systemic nocardiosis. Bacteremia is rare, although central line-associated bloodstream infections (CLABSIs) have been described, which require removal of the implicated catheter for cure.
Mycetoma, cutaneous nocardiosis, traumatic nocardiosis
Nocardial species can cause mycetoma, which typically manifests as a swollen area with sinuses draining purulent material. Primary cutaneous nocardiosis manifests as nontender, red, irregularly shaped raised lesions which may form sinus tracts and drain purulent material. Regional lymphadenopathy is uncommon. Nocardia arthritis usually presents as a monoarthritis, commonly involving the knee. Disease is often inoculated through a puncture wound, and may follow a contaminated intramuscular injection. Other inoculation nocardial infections described include postoperative wound infections, osteomyelitis, and keratitis.
Pulmonary nocardiosis
Pulmonary disease is apparent in 65% to 85% of systemic nocardial infections. The roentgenographic features include infiltrates that may cavitate, sometimes accompanied by empyema, pericarditis, or mediastinitis. There is no specific radiographic appearance, thus a high degree of suspicion must be maintained to make the diagnosis. Sputum cultures may be overgrown with other organisms before Nocardia colonies appear. Therefore, it may be helpful to notify the microbiology lab to use selective media and hold cultures for Nocardia if it is a suspected pathogen. Respiratory samples submitted for fungal culture are more likely to grow Nocardia than those submitted for mycobacterial (acid-fast bacillus [AFB]) culture.
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