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A09 — Infectious gastroenteritis and colitis, unspecified
A09
What this code means
Inflammation of the stomach and intestines, or of the colon, caused by an infection, with diarrhoea as the main symptom.
Also called: infectious gastroenteritis, infectious colitis, stomach bug.
When this code is used
Used when gastroenteritis or colitis is treated as infectious but no specific organism is identified.
Where it sits in ICD-10-CM
Code A09 belongs to Chapter 1: Infectious and parasitic diseases, which covers codes A00–B99 in the FY2027 ICD-10-CM tabular list. The official description above is copied verbatim from the CDC/NCHS FY2027 code file.
Related symptoms
Frequently asked questions
What is ICD-10-CM code A09?
A09 is the ICD-10-CM diagnosis code for “Infectious gastroenteritis and colitis, unspecified”. Inflammation of the stomach and intestines, or of the colon, caused by an infection, with diarrhoea as the main symptom.
When is code A09 used?
Used when gastroenteritis or colitis is treated as infectious but no specific organism is identified. It belongs to Chapter 1 of ICD-10-CM (Infectious and parasitic diseases).
This guide explains ICD-10-CM codes in plain language for patients, students and other readers. It is educational information only — not coding, billing or medical advice. The code recorded for any real encounter is assigned from the full clinical documentation by the treating team and qualified coders, and only they can decide which code fits a specific case.