• Clinical science



Actinomycosis is an infection caused by Actinomyces bacteria (especially Actinomyces israelii), which is ubiquitous in the oral cavity and is sometimes found in the gut or female genital tract. Actinomyces thrives in anaerobic environments, which are created by the proliferation of oxygen-consuming aerobic bacteria. The most frequent form of infection is cervicofacial actinomycosis, which occurs after injury to the oral cavity, face, or neck, although Actinomyces infection may also affect other parts of the body. The initial disease manifests as coarse, inflammatory nodules, which frequently develop into purulent, draining fistulae. Imaging enables a tentative diagnosis, but definitive diagnosis is based on culture and microscopic identification of Actinomyces. Antibiotics are used to treat actinomycosis and, in severe cases, surgery is required to remove lesions. Untreated cases of actinomycosis result in chronic, progressive disease.


  • Sex: > (3:1)
  • Peak incidence: adults (20–50 years)


Epidemiological data refers to the US, unless otherwise specified.



Predisposing factors

  • Poor dental hygiene , oral surgery (e.g., tooth extraction), local tissue inflammation (e.g., tonsillitis, tumor), comorbidities (e.g., diabetes) → cervicofacial actinomycosis
  • Intestinal surgery , foreign body ingestion, tumor → abdominal actinomycosis
  • Ascending infection from the uterus, associated with intra-uterine contraceptive devices → pelvic actinomycosis
  • History of aspiration, recent oral infection, or ongoing pulmonary malignancy (see aspiration pneumonia) → thoracic actinomycosis
  • Other primary sites of infection with hematogenous spread via the portal vein → hepatic actinomycosis (very rare)
  • Other primary sites of infection with hematogenous or contiguous spread to musculoskeletal (e.g., bone) or CNS (e.g., brain) tissue → musculoskeletal or neurological actinomycosis



Actinomyces is part of the normal flora of the oral cavity (less common in the lower gastrointestinal tract and female genital tract).

  • Mucosal injury (e.g., local trauma or surgery) → coexisting aerobic bacteria create an optimal anaerobic environment → proliferation of Actinomycespurulent, contiguous inflammation → formation of coarse granulation tissue and necrotic inclusions → possible fistula development
  • The neck, face, abdomen, pelvic, and lungs are the most common manifestations, although other locations are possible.

Actinomycosis infection spreads contiguously, with no regard for anatomical borders, and develops into multiple draining fistulae!


Clinical features

Cervicofacial actinomycosis (most frequent form of actinomycosis; 50–70% of all cases)

  • Slowly progressive mass in the neck and/or face; most commonly in the mandible region
  • Usually painless nodular lesions
  • Becomes indurated with purulent discharge that contains sulfur granules from fistulae and draining sinus tracts.
  • Canaliculitis: affects the lacrimal ducts or mouth, typically in the perimandibular region

Abdominal and pelvic actinomycosis (20% of all cases)

  • Fever, abdominal discomfort, changes in bowel habits
  • Possible pathological vaginal bleeding or discharge

Thoracic actinomycosis (15% of all cases)



Suspected cases based on the clinical presentation (e.g., presence of sulfur granules) can be confirmed via identification of the organism from tissue specimen (e.g., pus, biopsy tissue from suspected lesion) or sulfur granules.

  • Culture (confirmatory test)
  • Microscopy: direct visualization and staining of specimen; → accumulations of radially protruding and branching Actinomyces (conglomerates with a “cauliflower-like” appearance) that are surrounded by numerous granulocytes
  • Inflammatory markers: CRP, ESR
  • Spectrometry: molecular technique (e.g., matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF)

  • CT scan: assists in the identification of the exact location, extent of pathology, and/or guiding percutaneous aspiration of pus
  • Chest x-ray in thoracic actinomycosis
    • Poorly defined mass
    • Possible extension into pleura with thoracic disease

Definitive diagnosis is based on the identification of actinomycotic sulfur granules or bacteria!



  • Penicillin (drug of choice)
  • Surgical treatment for extensive or severe disease
    • Procedures
      • Incision and drainage of abscesses
      • Sinus tract excisions
      • Excision of recalcitrant fibrotic lesions



  • Adequate treatment often results in full recovery; however, early follow-up is required to identify possible recurrent infection.
  • Without treatment: chronic-progressive disease with contiguous spread; hematogenous spread is rare.