Actinomycosis is a rare, subacute-to-chronic bacterial infection caused by filamentous, gram-positive, non-acid-fast, anaerobic-to-microaerophilic bacteria of the genus Actinomyces — most commonly Actinomyces israelii in humans — characterized by contiguous (non-hematogenous) spread through tissue planes, suppurative and granulomatous inflammation, and the formation of multiple abscesses and draining sinus tracts that may discharge pathognomonic sulfur granules (yellow, grain-like bacterial aggregates). Unlike fungal infection, actinomycosis is a true bacterial infection despite its historical misclassification as a fungus due to the mold-like branching morphology of its colonies; it should not be confused with nocardiosis (Nocardia species), which is aerobic, acid-fast, and more commonly causes disseminated disease in immunocompromised hosts. The pathological mechanism involves mucosal barrier disruption — typically from dental trauma, surgery, aspiration of oral secretions, bowel perforation, or an intrauterine device (IUD) — that allows commensal Actinomyces (normally residing in the oropharynx, GI tract, and female genital tract) to invade deeper tissues and establish chronic infection. The four primary clinical forms encountered in coding are: cervicofacial (the most common, “lumpy jaw”; A42.2), thoracic/pulmonary (A42.0), abdominal (A42.1), and other/disseminated forms including actinomycotic meningitis (A42.81), encephalitis (A42.82), and sepsis (A42.7). Actinomycosis is frequently confused with malignancy on imaging due to its mass-like, infiltrating appearance; a key distinguishing feature is its indifference to anatomical boundaries and the simultaneous presence of sinus tracts discharging sulfur granules.
ETYMOLOGY of Actinomycosis
greek + new latin + german
Component
Origin
Meaning
actin- / actino-
Greek aktis (genitive aktinos) (ak-TEES)
“ray,” “beam of light,” “spoke of a wheel” — combining-form prefix describing the radiating, ray-like appearance of bacterial microcolonies
-mykes / -myco-
Greek mykēs (MOO-kays), from mykes (“mushroom, fungus”)
“fungus,” “mushroom” — historically applied because the branching hyphal colonies resembled mold, leading to the erroneous classification as a fungus
Noun-forming suffix — “condition of,” “diseased state of,” “process of” — indicates an abnormal pathological state
The word entered English in the 1870s as actinomycosis (noun), first recorded in 1877 per Merriam-Webster, borrowed from German Aktinomykose, derived from New Latin Actinomyces (the genus name) + German -ose (-osis). The genus Actinomyces was coined from Greek aktis (“ray”) + mykēs (“fungus”) — literally “ray fungus” — because the characteristic sulfur granules display a sunburst pattern of radiating filaments under microscopy. The root actin- (“ray”) connects actinomycosis to the broader actin- root family: actinium (actin- + -ium → radioactive element emitting rays), actinotherapy (actin- + therapy → treatment using radiation or light rays), and actinomycetes (ray-fungus organisms → the broader bacterial order). The suffix -myco- is highly productive in medical terminology and appears in mycology, mycosis, onychomycosis, dermatomycosis, and mycobacterium.
🔀 ALIASES / ALTERNATE TERMS
Actinomycotic(adjective form — appears in clinical collocations such as “actinomycotic abscess,” “actinomycotic sinus tract,” “actinomycotic meningitis”)
Lumpy jaw(lay and clinical term for cervicofacial actinomycosis; most commonly used in veterinary contexts for bovine infections caused by A. bovis, but also applied colloquially to the human cervicofacial form)
Sulfur granule disease(descriptive clinical synonym referencing the pathognomonic yellow granules discharged from sinus tracts; not a formal ICD-10-CM term but used in pathology and microbiology reports)
Cervicofacial actinomycosis(the most common form in humans, involving the jaw, neck, and face — typically following dental infection or trauma; coded A42.2)
Pulmonary actinomycosis(thoracic form arising from aspiration of oropharyngeal secretions; often mimics lung cancer or tuberculosis on imaging; coded A42.0)
Abdominal actinomycosis(GI/intraabdominal form; often follows appendicitis, diverticulitis, bowel perforation, or abdominal trauma; coded A42.1)
Pelvic actinomycosis(uterine/pelvic form strongly associated with long-term IUD use; may present as a pelvic mass mimicking ovarian cancer; coded A42.89)
Actinomycotic sepsis(systemic/disseminated form with hematogenous spread — rare but life-threatening; MCC-level severity; coded A42.7)
Actinomycotic meningitis(CNS form involving the meninges; coded A42.81)
Actinomycotic encephalitis(CNS form involving brain parenchyma; coded A42.82)
🔗 RELATED TERMS
Nocardiosis — the closest differential diagnosis to actinomycosis; caused by Nocardia species, which are aerobic, weakly acid-fast gram-positive filamentous bacteria; unlike actinomycosis, nocardiosis more commonly disseminates to the CNS and lungs in immunocompromised patients and does not produce sulfur granules (coded A43.x)
Sulfur granules — the pathognomonic finding of actinomycosis; yellow, grain-sized bacterial aggregates (1-2 mm) composed of Actinomyces filaments cemented by calcium phosphate; their presence in wound drainage strongly suggests actinomycosis
Actinomyces israelii — the most prevalent causative species in human actinomycosis; a commensal organism of the oropharynx, GI tract, and female genital tract that becomes pathogenic only after mucosal disruption
Sinus tract — a hallmark of chronic actinomycosis; a pathological channel connecting an abscess cavity to the skin surface or a hollow organ, through which purulent material (containing sulfur granules) is discharged
Granulomatous inflammation — the histopathological response characteristic of actinomycosis; involves the formation of granulomas (organized clusters of macrophages) around the bacterial colonies, contributing to the fibrotic, woody-hard tissue consistency
Suppurative inflammation — the complementary acute inflammatory response in actinomycosis involving neutrophil infiltration, pus formation, and abscess development — occurring simultaneously with granulomatous inflammation
Intrauterine device (IUD) — the primary risk factor for pelvic actinomycosis; long-term IUD use disrupts cervical/endometrial mucosal barriers, enabling Actinomyces colonization and subsequent infection
mycetoma — a chronic granulomatous infection of skin and subcutaneous tissue (caused by true fungi or actinomycetes) that may be confused with actinomycosis; distinguished by its primary cutaneous involvement and geographic distribution
Nocardia — a genus of aerobic, filamentous, weakly acid-fast gram-positive bacteria closely related to Actinomyces; important differential for pulmonary and disseminated actinomycosis
Actinomycetes — the broader order of filamentous, gram-positive bacteria that includes Actinomyces, Nocardia, Mycobacterium, and Corynebacterium; the term is often confused with Actinomyces (a single genus)
Gram-positive bacteria — the Gram stain classification of Actinomyces; gram-positive staining is an important distinguishing feature in laboratory identification
Anaerobe — Actinomyces species are anaerobic to microaerophilic, explaining why infections arise in poorly oxygenated deep tissue compartments following barrier disruption
CODING CORNER
🏥 ICD-10-CM CODES
Actinomycosis (A42) — Site-Specific Forms
Code
Description
A42.0
Pulmonary actinomycosis
A42.1
Abdominal actinomycosis
A42.2
Cervicofacial actinomycosis
A42.7
Actinomycotic sepsis
A42.81
Actinomycotic meningitis
A42.82
Actinomycotic encephalitis
A42.89
Other forms of actinomycosis (includes pelvic/uterine actinomycosis, cutaneous actinomycosis)
A42.9
Actinomycosis, unspecified
A42.-
Actinomycosis — parent category; NOT billable; shown for hierarchy reference only
Associated / Comorbid Conditions — Common Coding Companions
Code
Description
Z97.5
Presence of (intrauterine) contraceptive device (IUD) — relevant for pelvic actinomycosis
K37
Unspecified appendicitis — may be precipitating event for abdominal actinomycosis
K57.30
Diverticulosis of large intestine without perforation or abscess, without bleeding — common underlying etiology for abdominal form
J98.51
Empyema — may develop as complication of pulmonary actinomycosis
🔧 COMMON CPT CODES (Actinomycosis-Related Diagnosis & Treatment)
CPT Code
Description
87076
Culture, anaerobic isolate, additional methods required for definitive identification, each isolate (used when Actinomyces culture is positive to confirm species)
87143
Culture, typing; gas liquid chromatography (GLC) or high pressure liquid chromatography (HPLC) method (alternate Actinomyces identification method)
87149
Identification by nucleic acid (DNA or RNA probe), each organism (molecular identification of Actinomyces species)
86602
Antibody; actinomyces (serology — Actinomyces antibody titer for diagnosis)
87070
Culture, bacterial; any other source except urine, blood or stool, with isolation and presumptive identification of isolates (initial anaerobic culture for Actinomyces)
Excision of bone (eg, osteomyelitis or bone abscess); mandible (relevant for cervicofacial actinomycosis with mandibular bone involvement)
32035
Thoracostomy; with rib resection for empyema (for pulmonary actinomycosis complicated by empyema requiring rib resection/drainage)
⚠️ Coding Note: For actinomycosis coding, site specificity is mandatory — always assign the most specific A42.x code reflecting the documented anatomical site; defaulting to A42.9 (unspecified) is appropriate only when site is genuinely not documented and a provider query would be inappropriate given clinical context. Sequencing follows standard infection guidelines: when actinomycosis is the definitive confirmed diagnosis driving the admission, it sequences as the principal diagnosis, with any underlying precipitating condition (e.g., appendicitis, IUD presence, dental infection) coded as an additional diagnosis. A critical undercoding alert for inpatient profee coders: pelvic actinomycosis is frequently undercoded — when a female patient with a long-term IUD presents with a pelvic mass or abscess and Actinomyces is identified on pathology or culture, the correct code is A42.89 (Other forms of actinomycosis), NOT a generic pelvic abscess code; documentation trigger phrases to watch for include “IUD-associated infection,” “Actinomyces on Pap smear,” “pelvic mass with sulfur granules,” or “filamentous gram-positive rods in culture.”
ICD-10 CM A42.7 (Actinomycotic sepsis) carries MCC severity weight under MS-DRG v43.1, making it critical not to miss when sepsis criteria are met — verify provider documentation explicitly states “actinomycotic sepsis” or query for clarification when sepsis is present alongside a confirmed actinomycosis diagnosis.
For CPT coding of diagnostic cultures, note that 87076 is an add-on code to the initial culture and requires a positive result triggering additional identification methods; the base culture code (87070 or appropriate body-site-specific culture code) must be reported in addition.
# A Word from MedlinePlus:
Causes
Actinomycosis is usually caused by the bacterium called Actinomyces israelii. This is a common organism found in the nose and throat. It normally does not cause disease.
Because of the bacteria’s normal location in the nose and oral cavity, actinomycosis most commonly affects the face and neck. The infection can sometimes occur in the chest (pulmonary actinomycosis), abdomen, pelvis, or other areas of the body. The infection is not contagious. This means it does not spread to other people.
Symptoms occur when the bacteria enter the tissues of the face after trauma, surgery, or infection. Common triggers include dental abscess or oral surgery. The infection can also rarely affect women who have had an intrauterine device (IUD) to prevent pregnancy.
Once in the tissue, the bacteria cause 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 (pathway).
Symptoms
Symptoms may include any of the following:
Draining sores in the skin, especially on the chest wall from lung infection with Actinomyces
Fever
Mild or no pain
Swelling or a hard, red to reddish-purple lump on the face or upper neck
Weight loss
Exams and Tests
Your health care provider will perform a physical exam and ask about your symptoms.
Tests that may be done to check for the presence of the bacteria include:
The treatment of actinomycosis usually requires antibiotics for several months to a year. Surgical drainage or removal of the affected area (lesion) may be needed. If the condition is related to an IUD, the device must be removed.
Outlook (Prognosis)
Full recovery can be expected with treatment.
Possible Complications
In rare cases, meningitis can develop from actinomycosis. Meningitis is an infection of the membranes covering the brain and spinal cord. This membrane is called the meninges.
When to Contact a Medical Professional
Contact your provider if you develop symptoms of this infection. Starting treatment right away helps quicken the recovery.
Prevention
Good oral hygiene and regular dentist visits may help prevent some forms of actinomycosis.
Russo TA, Hu JC. Agents of actinomycosis. In: Blaser MJ, Cohen JI, Holland SM, et al, eds. Mandell, Douglas, and Bennett’s Principles and Practice of Infectious Diseases. 10th ed. Philadelphia, PA: Elsevier; 2026:chap 260.
Review Date 12/13/2025
Updated by: Jatin M. Vyas, MD, PhD, Roy and Diana Vagelos Professor in Medicine, Columbia University Vagelos College of Physicians and Surgeons, Division of Infectious Diseases, Department of Medicine, New York, NY. Also reviewed by David C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.
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