eMedicine Specialties > Infectious Diseases > Bacterial Infections

Nocardiosis

Author: Ronald A Greenfield, MD, Professor, Department of Internal Medicine, Section of Infectious Diseases, University of Oklahoma College of Medicine
Contributor Information and Disclosures

Updated: Oct 14, 2008

Introduction

Background

Nocardiosis is an acute, subacute, or chronic infectious disease that occurs in cutaneous, pulmonary, and disseminated forms. Primary cutaneous nocardiosis manifests as cutaneous infection (cellulitis or abscess), lymphocutaneous infection (sporotrichoid nocardiosis), or subcutaneous infection (actinomycetoma). Pleuropulmonary nocardiosis manifests as an acute, subacute, or chronic pneumonitis, usually in immunocompromised hosts, although isolated cases have been reported in immunocompetent hosts. Disseminated nocardiosis may involve any organ; lesions in the brain or meninges are most common.

Pathophysiology

Members of the genus Nocardia are aerobic actinomycetes that are ubiquitous saprophytes in soil, decaying organic matter, and water. At least 30 species of the genus Nocardia have been identified, and at least 13 of these are reported to cause human disease. New Nocardia species continue to be identified.¹ Nocardia asteroides is responsible for most cases of Nocardia disease among humans in the United States; various other Nocardia species are dominant in other parts of the world. Nocardia species also cause infections in animals, including bovine mastitis and sporotrichoid nocardiosis in horses.

When observed microscopically, either in Gram-stained smears of clinical specimens or cultures or on histopathology in tissues, Nocardia organisms are branching, beaded, filamentous, gram-positive bacteria with a characteristic morphology to a trained observer.

The cutaneous, lymphocutaneous, and subcutaneous forms of nocardiosis arise from local traumatic inoculation. These infections are not necessarily associated with immunocompromised host states, but dissemination from these sites of inoculation is more likely in immunocompromised hosts. Pleuropulmonary nocardiosis presumably arises from inhalation exposure. Disseminated nocardiosis results from hematogenous dissemination, usually from a pulmonary focus. Most persons with disseminated nocardiosis have underlying immunocompromising disease or are receiving immunosuppressive therapy.

Frequency

United States

In the 1970s, a survey estimated the incidence of nocardiosis in the United States at 500-1000 cases per year (0.4 cases per 100,000 population per year). However, with the increased prevalence of impaired cell-mediated immunity since then, the incidence of nocardiosis has likely also increased.³

Clusters of nocardiosis have been described in hospitalized patients, related to contaminated fomites from construction or contaminated hands of staff.¹

International

No reliable estimates on the international frequency of nocardiosis are available.

Mortality/Morbidity

Nocardiosis has a variable prognosis, depending on the site of infection, extent of infection, and underlying host factors.⁴

• Cure rates with appropriate therapy are approximately 100% in skin and soft-tissue infections.
• Ninety percent of pleuropulmonary infections can be cured with appropriate therapy.
• The cure rate in disseminated nocardiosis falls to 63%, while only half of patients with brain abscess can be cured with therapy.

Race

Nocardiosis has no apparent racial predilection.

Sex

Nocardiosis is more common in males than in females, with a male-to-female ratio of 3:1. This difference may be related to exposure frequency rather than a gender difference in susceptibility.

Age

All ages are susceptible to nocardiosis. The mean age at diagnosis is in the fourth decade of life.

Clinical

History

Clinical manifestations of nocardiosis depend on the site of infection.^{5,6,7,8,9,10,11,12,13,14,15,16}

• Primary cutaneous nocardiosis may present as cutaneous infection, lymphocutaneous infection, or subcutaneous infection.
  • Cutaneous nocardiosis generally manifests as either cellulitis or, more likely, single or multiple nontender erythematous nodule(s) at the site of traumatic inoculation. These nodules occasionally drain purulent material.
  • Lymphocutaneous nocardiosis manifests as similar lesions accompanied by ascending regional lymphadenopathy. The lymphadenopathy may also occasionally drain purulent material.
  • Nocardial species can cause mycetoma, a chronic, swollen, purulence-draining, subcutaneous infection of the extremities, typically encountered in tropical areas of the world.¹⁵
• Postoperative wound infections due to Nocardia species are rare.
• Traumatic inoculation nocardial arthritis has occurred but is rare. This presents as a subacute or chronic monarthritis, typically involving the knee.
• Traumatic inoculation nocardial endophthalmitis has also occurred in rare instances.
• Pulmonary disease is the predominant clinical finding in most patients with nocardiosis.^8,16
  • Pulmonary nocardiosis may be acute, subacute, or chronic.
  • Clinical manifestations include inflammatory endobronchial masses or localized or diffuse pneumonias, which may be accompanied by cavitation, abscess formation, pleural effusion, or empyema.
  • Symptoms in patients with nocardiosis are indistinguishable from those in patients with similar pulmonary infections of other microbial etiology. Cough with sputum production and fever are the dominant symptoms.
  • At least 40% of patients with disseminated nocardiosis have pulmonary infection; therefore, the clinical presentation may be dominated by the pulmonary symptoms.
• Patients with nocardiosis may present with deep abscess at any site, particularly in the lower extremities or the CNS. In patients with extra-CNS abscesses, fever and local symptoms predominate.
  • Up to 25% of nocardiosis cases (other than those involving mycetoma) involve the CNS. When occurring in isolation, CNS nocardiosis manifests as a slowly progressive mass lesion, with a host of specific neurologic findings related to the specific location of the abscess.
  • CNS nocardiosis is detected in 20-40% of disseminated nocardial infections. In two thirds of patients with CNS nocardiosis, clinical findings indicate abscess with or without meningitis, including fever, headache, stiff neck, and/or altered mental status.

Physical

The physical findings of nocardiosis also vary based on the site of infection.

• Patients with primary cutaneous nocardiosis present with cellulitis, cutaneous nodules, nodules with ascending lymphadenopathy, or with a mycetoma that is clinically indistinguishable from similar infections due to other pathogens.
• Patients with pulmonary nocardiosis present with findings of pulmonary consolidation with or without evidence of pleural effusions.
• The presentation of disseminated nocardiosis depends on the sites of infection.
  • Pulmonary findings frequently predominate.
  • Local findings associated with metastatic abscesses may be present at almost any site but are typically in the lower extremities. The combination of pneumonia and lower-extremity abscess is particularly suggestive of nocardiosis, although this is not seen exclusively in nocardiosis.
  • Patients with brain abscess may present with altered mental status, personality changes, or various localizing neurologic findings.
  • Patients with meningitis present with fever, altered consciousness, and meningismus.

Causes

Pulmonary and disseminated nocardiosis are clearly associated with immunocompromising conditions, with approximately 60% of cases of nocardiosis other than mycetoma occurring in individuals with some compromise of host defense systems. Conditions associated with an increased risk of pulmonary and disseminated nocardiosis include the following:

• Chronic pulmonary disease: Although pulmonary nocardiosis has been described in association with various chronic pulmonary diseases, patients with pulmonary alveolar proteinosis are at particular risk.
• Alcoholism
• Cirrhosis
• Lymphoreticular malignancy
• Solid-organ transplantation¹⁷
• Bone marrow or stem cell transplantation
• Long-term corticosteroid use or Cushing syndrome
• Systemic lupus erythematosus
• Systemic vasculitis
• Ulcerative colitis
• Sarcoidosis
• Renal failure
• Whipple disease
• Hypogammaglobulinemia
• Treatment with anti–tumor necrosis factor antibody
• HIV infection and AIDS: Nocardiosis in individuals with advanced HIV disease usually presents as a relentlessly progressive infiltrative pulmonary infection. The median CD4 count in patients infected with HIV who develop nocardiosis is approximately 50 cells/µL.¹³

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