ICD-10 Code A42.9 – Actinomycosis, unspecified (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code A42.9 – Actinomycosis, unspecified
What it is
A42.9 identifies actinomycosis when the site or specific form is not documented. It refers to a chronic bacterial infection caused by Actinomyces species.
Clinical signs
Clinical features vary; refer to documentation. Typical findings may include slowly progressive swelling, abscess formation, draining sinuses, or involvement of the cervicofacial, thoracic, or abdominal regions.
When to use this code
Use A42.9 when the provider documents actinomycosis but does not specify the anatomic site or another more specific subtype. It also fits when the record confirms actinomycosis and the details needed for a more precise code are absent. If the chart names a specific location, code that site instead.
Do not use for
Do not use this code for a specified actinomycosis site when a more precise ICD-10 code is available. Check documentation if the diagnosis is only suspected, ruled out, or described under another infection.
Coding tip
Query for the affected site before defaulting to A42.9; unspecified coding is appropriate only when the record lacks further detail.