2026 ICD-10-CM Diagnosis Code A09Infectious gastroenteritis and colitis, unspecified

ICD-10-CM Codes›A00–B99›A00-A09›A09

ICD-10-CM A09
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

A09 is a billable ICD-10-CM diagnosis code for infectious gastroenteritis and colitis, unspecified. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 391 through 392. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Intestinal infection; and Parasitic, other specified and unspecified infections.

Code Identity

ICD-10-CM Code
A09
Billable Status
Yes — Valid for Submission
Code Describes
Infectious gastroenteritis and colitis, unspecified
Chapter
A00-A09
Intestinal infectious diseases

Code Classification

ChapterA00–B99Certain infectious and parasitic diseases
SectionA00-A09Intestinal infectious diseases
CategoryA09Infectious gastroenteritis and colitis, unspecified
This CodeA09Infectious gastroenteritis and colitis, unspecified

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Acute erosive gastritis
  • Acute gastroenteritis
  • Acute infectious nonbacterial gastroenteritis
  • Acute infective gastroenteritis
  • Acute ulcerative gastroenteritis complicating pneumonia
  • Aspergillosis enteritis of intestine
  • Aspergillus colitis
  • Blastomycotic enteritis of intestine
  • Catarrhal dysentery
  • Colitis presumed infectious
  • Colitis, enteritis and gastroenteritis presumed infectious
  • Diarrhea of presumed infectious origin
  • Disease caused by Heterocheiloidea
  • Disease of presumed infectious origin
  • Disorder of gastrointestinal tract co-occurrent with human immunodeficiency virus infection
  • Dysenteric diarrhea
  • Enteritis of intestine presumed infectious
  • Enteritis of small intestine presumed infectious
  • Epidemic diarrhea
  • Epidemic gastroenteritis
  • Erosive gastritis
  • Fungal colitis
  • Fungal duodenitis
  • Fungal gastrointestinal infection
  • Gastroenteritis presumed infectious
  • Gastrointestinal infection
  • Herpes simplex gastrointestinal tract infection
  • Infection by Anisakidae
  • Infection by Anisakis larva
  • Infection by Blastomyces dermatitidis
  • Infection of digestive system
  • Infection of intestine caused by Anisakis larva
  • Infection of large intestine
  • Infectious colitis
  • Infectious diarrheal disease
  • Infectious disease of digestive tract
  • Infectious enteritis of intestine
  • Infectious gastroenteritis
  • Infectious gastroenteritis co-occurrent with human immunodeficiency virus infection
  • Infectious gastroenteritis with AIDS
  • Infective gastritis
  • Institution-acquired gastroenteritis
  • Institutional environment related disease
  • Intestinal infectious disease
  • Phlegmonous enteritis of gastrointestinal tract
  • Purulent enteritis
  • Secondary acquired megacolon
  • Suppurative gastritis
  • Toddler diarrhea
  • Toxic megacolon due to infectious colitis
  • Toxic state
  • Toxic state due to colonic dilatation

Tabular List NotesGuidance

Coding notes and annotation back-references applicable to this code.

Inclusion Terms

  • Infectious colitis NOS
  • Infectious enteritis NOS
  • Infectious gastroenteritis NOS

Type 1 Excludes

  • colitis NOS K52.9
  • diarrhea NOS R19.7
  • enteritis NOS K52.9
  • gastroenteritis NOS K52.9
  • noninfective gastroenteritis and colitis, unspecified K52.9

Index to Diseases and InjuriesGuidance

Alphabetical index entries that point to this code.

External Cause of Injuries IndexGuidance

References for this code in the External Cause of Injuries Index.

    • Arthritis, arthritic(acute) (chronic) (nonpyogenic) (subacute)
      • in (due to)
        • enteritis, infectious NEC
    • Colitis(acute) (catarrhal) (chronic) (noninfective) (hemorrhagic)
      • regional
        • infectious
    • Diarrhea, diarrheal(disease) (infantile) (inflammatory)
      • dysenteric
    • Diarrhea, diarrheal(disease) (infantile) (inflammatory)
      • endemic
    • Diarrhea, diarrheal(disease) (infantile) (inflammatory)
      • epidemic
    • Diarrhea, diarrheal(disease) (infantile) (inflammatory)
      • infectious
    • Disease, diseased
      • diarrheal, infectious NEC
    • Dysentery, dysenteric(catarrhal) (diarrhea) (epidemic) (hemorrhagic) (infectious) (sporadic) (tropical)
    • Dysentery, dysenteric(catarrhal) (diarrhea) (epidemic) (hemorrhagic) (infectious) (sporadic) (tropical)
      • arthritis
    • Enteritis(acute) (diarrheal) (hemorrhagic) (noninfective)
      • epidemic (infectious)
    • Enteritis(acute) (diarrheal) (hemorrhagic) (noninfective)
      • infectious NOS
    • Enteritis(acute) (diarrheal) (hemorrhagic) (noninfective)
      • septic
    • Enterocolitis
      • infectious NEC
    • Gastroenteritis(acute) (chronic) (noninfectious)
      • epidemic (infectious)
    • Gastroenteropathy
      • infectious
    • Ileitis(chronic) (noninfectious)
      • infectious
    • Ileocolitis
      • infectious
    • Sigmoiditis
      • infectious
    • Ulcer, ulcerated, ulcerating, ulceration, ulcerative
      • dysenteric

Clinical ClassificationClinical

AHRQ’s CCSR groups this code into broader clinical categories.

CCSR DIG001
Intestinal infection
Default principal diagnosis: inpatient Yes · outpatient Yes
CCSR INF009
Parasitic, other specified and unspecified infections
Default principal diagnosis: inpatient No · outpatient No

Clinical InformationClinical

  • Erosive Gastritis

    gastritis that is characterized by erosion of the mucosal surface.

  • Infectious Colitis

    a viral or bacterial infectious process affecting the large intestine.

Patient EducationClinical

Gastroenteritis

Gastroenteritis is an inflammation of the lining of the stomach and intestines. The main symptoms include vomiting and diarrhea. It is usually not serious in healthy people, but it can sometimes lead to dehydration or cause severe symptoms.

The full article covers:

  • What is gastroenteritis?
  • What causes gastroenteritis?
  • What are the symptoms of gastroenteritis?
  • How is gastroenteritis diagnosed?
  • What are the treatments for gastroenteritis?
  • Can gastroenteritis be prevented?

Read the full article at MedlinePlus

Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.

Convert A09 to ICD-9-CMHistory

The closest ICD-9-CM equivalents under the General Equivalence Mappings.

ICD-9-CM
009.0 Infectious enteritis NOS
Approximate The match is approximate rather than exact.

Code HistoryHistory

FY 2016AddedAdded to the ICD-10-CM code setEffective October 1, 2015, the first year of ICD-10-CM.
FY 2017–2025No changes
FY 2026CurrentCurrent code set, no changesEffective October 1, 2025 through September 30, 2026.

Questions About A09Overview

Is A09 (Infectious gastroenteritis and colitis, unspecified) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report infectious gastroenteritis and colitis, unspecified on HIPAA-covered claims from October 1, 2025 through September 30, 2026.

What MS-DRG does A09 group to?

When infectious gastroenteritis and colitis, unspecified is the principal diagnosis on an inpatient stay, it groups to MS-DRG 391, 392, with relative weights from 0.7796 to 1.2683 depending on complications. Higher weights mean higher Medicare reimbursement.

What is the ICD-9 equivalent of A09?

Under the General Equivalence Mappings, infectious gastroenteritis and colitis, unspecified converts to ICD-9-CM 009.0 (infectious enteritis NOS). The mapping is approximate, so confirm the match fits the documentation.

Footnotes

[1] Not chronic - A diagnosis code that does not fit the criteria for chronic condition (duration, ongoing medical treatment, and limitations) is considered not chronic. Some codes designated as not chronic are acute conditions. Other diagnosis codes that indicate a possible chronic condition, but for which the duration of the illness is not specified in the code description (i.e., we do not know the condition has lasted 12 months or longer) also are considered not chronic.