The 3 major anatomic types of disease are cervicofacial, thoracic, and abdominal. Cervicofacial lesions are the most common and often occur after tooth extraction, oral surgery, or facial trauma or are associated with carious teeth. Localized pain and induration progress to "woody hard" nodular lesions that can be complicated by draining sinus tracts that usually are located at the angle of the jaw or in the submandibular region. The infection usually spreads by direct invasion of adjacent tissues. Infection also may contribute to chronic obstructive tonsillitis. Thoracic disease most commonly is secondary to aspiration of oropharyngeal secretions and occurs rarely after esophageal disruption secondary to surgery or nonpenetrating trauma or may be an extension of cervicofacial infection. Disease manifests as pneumonia, which can be complicated by abscesses, empyema, and rarely, pleurodermal sinuses. Focal or multifocal masses may be mistaken for tumors. Abdominal actinomycosis usually is attributable to penetrating trauma or intestinal perforation. The appendix and cecum are the most common sites, and symptoms are similar to those of appendicitis. Slowly developing masses may simulate abdominal or retroperitoneal neoplasms. Intra-abdominal abscesses and peritoneal-dermal draining sinuses occur eventually. Chronic localized disease often forms sinus tracts that drain a purulent discharge. Other sites of actinomycosis infection include the liver, pelvis (which, in some cases, has been linked to use of intrauterine devices), and brain. Primary cutaneous actinomycosis also has been reported.

Etiology

Actinomyces israelii is the usual cause. A israelii and at least 5 other Actinomyces species are slow-growing, microaerophilic or facultative anaerobic, gram-positive, filamentous branching bacilli that can be part of the normal oral, gastrointestinal, or vaginal flora. Actinomyces species frequently are copathogens in tissues harboring multiple species. Actinobacillus actinomycetemcomitans is a frequent copathogen, and its isolation may predict the presence of actinomycosis.

Epidemiology

Actinomyces species are worldwide in distribution. The organisms are components of the endogenous oral and gastrointestinal tract flora. Actinomyces species are opportunistic pathogens, and disease results from penetrating (including human bite wounds) and nonpenetrating trauma. Infection is rare in infants and children. Overt, microbiologically confirmed, monomicrobial disease caused by Actinomyces species has become rare in the era of antimicrobial agents.

The incubation period varies from several days to several years.

Diagnostic Tests

A microscopic demonstration of beaded, branched, gram-positive bacilli in purulent material or tissue specimens suggests the diagnosis. The specimen should be taken only from a normally sterile site. Acid-fast staining can be used to distinguish Actinomyces species, which are acid-fast negative, from Nocardia species, which are variably acid-fast positive. "Sulfur granules" in drainage or loculations of purulent material usually are yellow and may be visualized microscopically or macroscopically and suggest the diagnosis when present. A Gram stain of sulfur granules discloses a dense reticulum of filaments. Immunofluorescent stains for Actinomyces species are available. Actinomyces species can be identified in tissue specimens using the 16s rRNA sequencing and polymerase chain reaction assay. Although most Actinomyces species are microaerophilic or facultative anaerobic, specimens must be obtained, transported, and cultured anaerobically on semiselective media.

Treatment

Initial therapy should include intravenous penicillin G or ampicillin for 4 to 6 weeks followed by high doses of oral penicillin (up to 2 g/day for adults) for a total of 6 to 12 months. Amoxicillin, erythromycin, clindamycin, doxycycline, and tetracycline are alternative antimicrobial choices. Tetracyclines are not recommended for pregnant women or children younger than 8 years of age. Surgical drainage often is a necessary adjunct to medical management and may allow for a shorter duration of antimicrobial Treatment.

Isolation of the Hospitalized Patient

Standard precautions are recommended. There is no person-to-person spread.

Control Measures

Appropriate oral hygiene, regular dental care, and careful cleansing of wounds, including human bite wounds, can prevent infection.