Definition of Actinomycosis:

Actinomycosis is a long-term (chronic) bacterial infection that commonly affects the face and neck.

Causes, incidence, and risk factors:

Actinomycosis is usually caused by an anaerobic bacteria called Actinomyces israelii, which is a common and normally not disease-causing (nonpathogenic) organism found in the nose and throat.

Because of the bacteria's normal location in the nose and throat, actinomycosis most commonly appears in the face and neck. The infection is not contagious.

Symptoms occur when the bacteria enters the facial tissues after trauma, surgery, or infection. A common cause is dental abscess or oral surgery. Once in the tissue, it forms an abscess, producing a hard, red to reddish-purple lump, often on the jaw, from which comes the condition's common name, "lumpy jaw."

Eventually, the abscess breaks through the skin surface to produce a draining sinus tract. Actinomycosis can sometimes occur in the chest (pulmonary actinomycosis) and abdomen or other areas of the body.