2027 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 2027 ICD-10-CM dataset · Effective Oct 1, 2026 – Sep 30, 2027

A09 is a billable ICD-10-CM diagnosis code for infectious gastroenteritis and colitis, unspecified. It is valid on HIPAA claims for fiscal year 2027 (October 1, 2026 through September 30, 2027) and groups to MS-DRG 391 through 392. As a secondary diagnosis, it counts as a complication or comorbidity (CC) and moves an inpatient stay to a higher severity level within its MS-DRG family. It does not count, however, when the principal diagnosis is one of 81 closely related codes. 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
Short Description
Infectious gastroenteritis and colitis, unspecified
Same as the full description in the CMS dataset.
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
  • Recurrent infection of gastrointestinal tract
  • Secondary acquired megacolon
  • Suppurative gastritis
  • Toddler diarrhea
  • Toxic megacolon due to infectious colitis
  • Toxic state
  • Toxic state due to colonic dilatation

Instructional NotesGuidance

Instructions from the official ICD-10-CM Tabular List that apply to A09: its own notes plus those printed at Chapter 1. A note printed at a category, block or chapter applies to every code under it.

Includes

Further defines, or gives examples of, the content of the category.

From Chapter 1 (A00-B99) Certain infectious and parasitic diseases applies to 1,068 codes
  • diseases generally recognized as communicable or transmissible

Applicable To

Conditions this code is used for: synonyms of the title or, for "other specified" codes, the conditions assigned to it. The list is not exhaustive.

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

Excludes1

Not coded here: the excluded code is never reported together with this one, unless the two conditions are unrelated.

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

Excludes2

Not included here: the excluded condition is not part of this code, but a patient may have both, so both codes may be reported.

From Chapter 1 (A00-B99) Certain infectious and parasitic diseases applies to 1,068 codes
  • carrier or suspected carrier of infectious disease (Z22.-)
  • certain localized infections - see body system-related chapters
  • infectious and parasitic diseases complicating pregnancy, childbirth and the puerperium (O98.-)
  • infectious and parasitic diseases specific to the perinatal period (P35-P39)
  • influenza and other acute respiratory infections (J00-J22)

Use Additional Code

Add a second code, after this one, to fully describe the condition.

From Chapter 1 (A00-B99) Certain infectious and parasitic diseases applies to 1,068 codes
  • code to identify resistance to antimicrobial drugs (Z16.-)

Source: CMS ICD-10-CM Tabular List. How to read instructional notes.

Referenced in Other NotesGuidance

Instructional notes printed at other codes that name A09, its category, or a range that includes it.

Excludes1 1

These codes carry an Excludes1 note naming A09: they are not reported together with it, unless the two conditions are unrelated.

  • K52.9 Noninfective gastroenteritis and colitis, unspecified
    infectious gastroenteritis and colitis NOS (A09)

Excludes2 2

These codes carry an Excludes2 note naming A09: its condition is not part of those codes, and both may be reported when the patient has both.

  • Block P35-P39 Infections specific to the perinatal period
    intestinal infectious disease (A00-A09) names A00-A09, which includes this code
  • P37 Other congenital infectious and parasitic diseases
    infectious neonatal diarrhea (A00-A09) names A00-A09, which includes this code

Index to Diseases and InjuriesGuidance

Alphabetical index entries that point to this code.

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

  • Dysentery

    acute inflammation of the intestine associated with infectious diarrhea of various etiologies, generally acquired by eating contaminated food containing toxins, biological derived from bacteria or other microorganisms. dysentery is characterized initially by watery feces then by bloody mucoid stools. it is often associated with abdominal pain; fever; and dehydration.

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 2017–2026No changes
FY 2027CurrentCurrent code set, no changesEffective October 1, 2026 through September 30, 2027.

Questions About A09Overview

What is the ICD-10 code for infectious gastroenteritis and colitis, unspecified?

The ICD-10-CM code for infectious gastroenteritis and colitis, unspecified is A09. It is billable on HIPAA-covered claims from October 1, 2026 through September 30, 2027.

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, 2026 through September 30, 2027.

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 392, 391, with relative weights from 0.7645 to 1.2389 depending on complications. Higher weights mean higher Medicare reimbursement.

Is A09 a CC or MCC?

CMS lists A09 as a CC (complication or comorbidity) for FY 2027. Reported as a secondary diagnosis, it moves the inpatient stay to a higher-weighted DRG within its severity family. It does not count when the principal diagnosis is one of the 81 closely related codes in its exclusion list.

Can A09 be reported with K52.9?

Not as a rule. The Excludes1 note on A09 lists "colitis NOS (K52.9)". An Excludes1 note means the excluded code is never reported together with this one; the only exception is when the two conditions are unrelated to each other (Official Guidelines, Section I.A.12.a).