A09 ICD-10-CM Code: Infectious gastroenteritis and colitis, unspecified
HCC Buddy Code Card
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FY 2026 Apr update / Certain infectious and parasitic diseases (A00-B99) / Intestinal infectious diseases (A00-A09)
A09
Billable / SpecificICD-10-CMOfficial ICD-10-CMCodebook guidanceInfectious gastroenteritis and colitis, unspecified
This code describes inflammation of the stomach and intestines caused by an infection, when the specific cause (like bacteria or virus) is not identified or documented. It's commonly known as infectious diarrhea or food poisoning.
CMS-HCC V28
N/A—
Not mapped
CMS-HCC V24
N/A—
Not mapped
ACA/HHS
N/A—
Not mapped
ESRD/PACE
N/A—
Not mapped
RXHCC
N/A—
Not mapped
Code Book Path
Inclusion Terms
Official- Infectious colitis NOS
- Infectious enteritis NOS
- Infectious gastroenteritis NOS
Excludes 2
OfficialICD-10-CM does not list Excludes 2 notes for A09 in this effective period.
Related Child Codes
ICD-10-CM does not list child codes under A09 for this display context.
Includes
OfficialICD-10-CM does not list Includes notes for A09 in this effective period.
Excludes 1
Official- colitis NOS (K52.9)
- diarrhea NOS (R19.7)
- enteritis NOS (K52.9)
- gastroenteritis NOS (K52.9)
- noninfective gastroenteritis and colitis, unspecified (K52.9)
Code First
OfficialICD-10-CM does not list Code First sequencing instructions for A09 in this effective period.
Use Additional
OfficialICD-10-CM does not list Use Additional Code instructions for A09 in this effective period.
Code Also
OfficialICD-10-CM does not list Code Also instructions for A09 in this effective period.
Buddy Documentation Tip
Last updated: FY2026 ICD-10-CM Apr update, Apr 1, 2026 through Sep 30, 2026. CMS-HCC V28 is 100% phased in for payment year 2026.
Is A09 an HCC code?
No. A09 is a billable ICD-10-CM code but does not map to any HCC category in V28, V24, ESRD, or RxHCC.
Coder workflow notes
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This code does not map to an HCC category in any model (V28, V24, ESRD, RxHCC).
What This Code Means
A09 is the ICD-10-CM diagnosis code for infectious gastroenteritis and colitis, unspecified. This code describes inflammation of the stomach and intestines caused by an infection, when the specific cause (like bacteria or virus) is not identified or documented. It's commonly known as infectious diarrhea or food poisoning. A09 sits in the ICD-10-CM chapter for certain infectious and parasitic diseases (a00-b99), within the section covering intestinal infectious diseases (a00-a09).
A09 is a billable ICD-10-CM code but does not map to a payment HCC under the CMS-HCC V28, V24, ESRD, or RxHCC risk adjustment models. It can be reported on Medicare Advantage encounter data submissions but it does not contribute to a beneficiary's RAF score and therefore does not affect risk-adjusted payments to the plan.
Use this code only when the infectious agent is truly unknown or unspecified; if the causative organism is identified (e.g., Salmonella, Norovirus), use the more specific code instead.
HCC Buddy maintains structured V28 and V24 mapping, RAF weights, and MEAT documentation criteria for A09 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •Use this code only when the infectious agent is truly unknown or unspecified; if the causative organism is identified (e.g., Salmonella, Norovirus), use the more specific code instead
- •This code includes both gastroenteritis and colitis presentations; document the clinical presentation and any identified symptoms to support medical necessity