Actinomyces odontolyticus Breast Abscess

To the Editor:

A 40-year-old female presented with a 2-wk history of a tender right breast mass that was increasing in size. She complained of constant, severe breast pain. She stated that the mass had grown in size during the week before her presentation. Her last mammogram was two years earlier and had reportedly been normal. She had a remote history of smaller left breast masses that had resolved spontaneously ∼10 years ago; at that time an ultrasound examination was done and had been normal according to the patient. She did not have any notable past medical or surgical history, was not taking any medications, was a non-smoker, and denied any family history of breast cancer. The patient had no history of pregnancy or lactation. The patient worked as a visiting nurse, but reported no recent care of open wounds or of persons with communicable diseases. The patient was active sexually but reported no bites to the breast.

On physical examination the patient was afebrile with normal vital signs. There was a 3-cm indurated, tender, irregular mass in the lower inner quadrant of her right breast, just above the inframammary fold. There was overlying erythema of 9 cm diameter and a central fluctuant area, but no central area of necrosis. There were no signs of spontaneous drainage, trauma, or an insect bite.

The mass was incised and drained, with the retrieval of 10 mL of purulent fluid that was sent for culture. The patient was treated with oral cephalexin with only slight improvement of the erythema and induration in her breast over the following week. Culture identified Actinomyces odontolyticus in the fluid from her breast mass. Her antibiotic was changed to penicillin V potassium, with complete resolution and healing of her breast mass over the next 2 wks.

Actinomyces spp. are gram-positive bacilli, either anaerobic or aero-tolerant, that are identified increasingly as a cause of human infection. They are typically isolated from the mucous membranes of the gastrointestinal tract, female genital tract, and oropharynx. The suppurative infections caused in these locations by Actinomyces spp. are classically chronic and associated with the development of sinus tracts.

Abscesses of the breast occur frequently, and are often caused by typical cutaneous or oral flora, most commonly Staphylococcus aureus. They can be either primary and caused by a disruption of the skin adjacent to the areola, or secondary and caused by the hematogenous spread of a pathogenic organism from a distant organ [1]. Mammary duct obstruction can also lead to bacterial growth and abscess formation. Actinomycosis causing breast abscesses has been described infrequently, with Actinomyces israelii being the causative organism most commonly [2,3]. Additionally, primary breast abscesses caused by A. viscosus, A. turicensis, A. eurpaeus, A. meyerii, A. neuii, and A. radingae have been reported [1,4–7]. The patients in these reports are females presenting with a mass causing concern about carcinoma, a draining sinus tract, or a recurrent or persistent abscess or both. The recommended treatment is surgical drainage of the abscess along with a prolonged course of treatment with penicillin.

Actinomyces odontolyticus, an organism found commonly in the oral cavity, is a facultative anaerobe, discovered originally in dental caries. It is encountered rarely as a human pathogen. Limited case reports describe A. odontolyticus as the causative organism of solid-organ abscesses including abscesses of the liver or brain, of pleuropericardial infection, and of bacteremia [8–11]. To our knowledge, ours is the first report of a primary breast abscess caused by A. odontolyticus.

Breast abscesses secondary to actinomycosis are rare, but should be considered when an infection does not improve clinically with usual antimicrobial therapy. A deep culture should be obtained at the time of initial drainage of such an abscess, and a prolonged course of treatment with penicillin is recommended.