Alphabetic Index FY2027

A09

Infectious gastroenteritis and colitis, unspecified

FY2027Chapter 1: Certain infectious and parasitic diseases/A00–A09 Intestinal infectious diseases

BillableComplete code, valid to report
Care settingsHome Health Primary · MMTA - Infectious Disease, Neoplasms, and Blood-Forming DiseasesHospital CC

A09 is a billable ICD-10-CM diagnosis code for infectious gastroenteritis and colitis, unspecified. It is part of the FY2027 code set, effective October 1, 2026. The Alphabetic Index lists it under 19 entries. Its coding notes include a Use additional code instruction, 5 Excludes1 entries and 5 Excludes2 entries.

Use additional code

Add the listed code as a secondary code, if known.

Also from chapter/block level (1 note)
Inherited from Chapter 1 Certain infectious and parasitic diseases
  • code to identify resistance to antimicrobial drugs (Z16.-)

Excludes1

Not coded here. The listed conditions generally should not be reported together.

This code
  • 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. Both codes may be reported if the patient has both conditions.

Also from chapter/block level (5 notes)
Inherited from Chapter 1 Certain infectious and parasitic diseases
  • 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)

Care settings

How CMS programs treat this code. These are CMS claim edits and list entries, not coverage or eligibility rules.

Home Health Primary

Accepted as the primary (principal) diagnosis on a home health claim. The Home Health Grouper assigns it to the MMTA - Infectious Disease, Neoplasms, and Blood-Forming Diseases clinical group.

Source: CMS Home Health Grouper Software v07.2.26, effective October 1, 2026

Hospital CC

Counts as a complication or comorbidity (CC) when reported as a secondary diagnosis on an inpatient claim. It does not count when the principal diagnosis is one of the 81 codes in its exclusion list. Some MS-DRGs also ignore a CC or MCC that defines the DRG.

Source: CMS MS-DRG Definitions Manual v44, effective October 1, 2026, Appendix C

Includes

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

Also from chapter/block level (1 note)
Inherited from Chapter 1 Certain infectious and parasitic diseases
  • diseases generally recognized as communicable or transmissible

Inclusion terms

Conditions classified to this code.

This code
  • Infectious colitis NOS
  • Infectious enteritis NOS
  • Infectious gastroenteritis NOS

Alphabetic Index terms

Terms the official Alphabetic Index lists for this code. 19 entries

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