Actinomyces and Nocardia Species

Indications for Testing

Pulmonary cavitary disease, cervicofacial abscesses

Laboratory Testing

Actinomycosis
- Specimen must be collected and transported under anaerobic conditions
- May require aggressive collection methods (eg, needle biopsy, transbronchial biopsy)
Nocardiosis
- Gram stain and modified acid-fast stain of sputum or infected material
- Culture from infected site – make take up to 2 weeks to grow; lab should be notified of suspicion so culture is maintained at >48-72°

Histology

Actinomycosis
- Sulphur granules occasionally noted in infected material

Imaging Studies

Chest x-ray
- Actinomycosis
  - Cavitation coupled with soft tissue swelling and rib involvement
  - Most common in lower lobes
- Nocardiosis
  - Cavitation
  - May appear as masses, nodules, consolidation

Differential Diagnosis

Pulmonary manifestations
- Bacteria
  - Mycobacteria spp
  - Gram negative organisms
  - Rhodococcus equi
- Lung abscess
- Lung cancer
- Fungal
  - Aspergillus
  - Cryptococcus
Cervical-facial manifestations
- Lymphadenitis
- Neoplasm
  - Local – head and neck
  - Metastatic
- Tonsillitis
- Necrotic skin infection
- Other odontogenic infections
Abdominal manifestations
- Appendicitis
- Diverticulitis
- Peptic ulcer disease
- Foreign body/obstruction
- Malignancy
- Inflammatory bowel disease

Actinomyces and Nocardia species are the causative agents of actinomycosis and nocardiosis; these are often considered when patients develop indolent granulomatous diseases.

Epidemiology

Incidence
- Actinomycosis – 1-2/300,000
- Nocardiosis – <1/300,000
Age
- Actinomycosis – peaks in 40s-50s
- Nocardiosis – all ages but rare in children
Sex
- Actinomycosis – M>F, 3:1
- Nocardiosis – M>F
Transmission
- Actinomycosis
  - Mucosal barrier disruption with contiguous spread
  - Aspiration
- Nocardiosis – inhalation or direct inoculation (eg, penetrating injury)

Organisms

Actinomyces
- Facultative anaerobe
  - Gram-positive
  - Non-spore forming
  - Commensal of the human oropharynx gastrointestinal tract and female genitalia
- Disease most commonly caused by A. israelii
  - Infection may be associated with IUD use
- Most infections are polymicrobial
Nocardia
- Aerobic genus of the order Actinomycetaceae
  - Gram-positive
  - Weakly acid-fast
  - Soil saprophytes
- Disease mainly caused by species in the former N. asteroides complex
  - Most commonly N. cyriacigeorgica

Risk Factors

Actinomycosis
- Alcoholism
- Poor oral hygiene
- Pulmonary form – emphysema, chronic bronchitis, bronchiectasis
Nocardiosis
- Alcoholism
- Diabetes mellitus
- HIV
- Immunocompromised state – particularly solid organ transplant patients
- Trauma

Clinical Presentation

Actinomycosis
- Usually has insidious onset with constitutional symptoms – fever, anorexia, malaise, weight loss
- Oral-cervicofacial – most frequent location
  - Soft tissue swelling, abscess or mass lesion
    - Most common in premandibular region
    - Sinus tracts occur frequently
- Thoracic disease
  - Slowly progressive pneumonia
  - May also involve pleura, mediastinum, chest wall, pericardium
- Abdominal disease
  - Appendicitis, perirectal disease, hepatic infection, pelvic disease, renal disease
Nocardiosis
- Predominantly causes pneumonia
  - Irregular nodular disease
  - May progress to cavitary disease
  - Process may resemble tuberculosis
- Disseminated disease common
  - Cerebral abscess – occurs in ~30% of patients with pulmonary disease
  - Other sites – eyes, kidney, bones, joints, heart
- Skin and soft tissue infections, lymphadenitis – usually result from trauma
- Bacteremia – often catheter-related
- Peritonitis – usually peritoneal-dialysis-catheter-related
- Local spread of disease – chest wall, soft tissue masses, bone destruction and external fistulas