2026 ICD-10-CM Diagnosis Code A04.9Bacterial intestinal infection, unspecified

ICD-10-CM Codes›A00–B99›A00-A09›A04

ICD-10-CM A04.9
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

A04.9 is a billable ICD-10-CM diagnosis code for bacterial intestinal infection, unspecified. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 371 through 373. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Bacterial infections and Intestinal infection.

Code Identity

ICD-10-CM Code
A04.9
Billable Status
Yes — Valid for Submission
Code Describes
Bacterial intestinal infection, unspecified
Short Description
Bacterial intestinal infection, unspecified
Same as the full description in the CMS dataset.
Parent Code
A04
Other bacterial intestinal infections

Code Classification

ChapterA00–B99Certain infectious and parasitic diseases
SectionA00-A09Intestinal infectious diseases
CategoryA04Other bacterial intestinal infections
This CodeA04.9Bacterial intestinal infection, unspecified

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Bacterial dysentery
  • Bacterial enteritis of intestine
  • Bacterial gastroenteritis
  • Bacterial gastrointestinal infectious disease
  • Bacterial intestinal infectious disease
  • Bacterial overgrowth syndrome
  • Colitis caused by bacterium
  • Dysenteric diarrhea
  • Emphysematous gastritis
  • Purulent enteritis
  • Small bowel bacterial overgrowth syndrome
  • Suppurative colitis

Tabular List NotesGuidance

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

Inclusion Terms

  • Bacterial enteritis NOS

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.

    • Diarrhea, diarrheal(disease) (infantile) (inflammatory)
      • due to
        • bacteria
    • Enteritis(acute) (diarrheal) (hemorrhagic) (noninfective)
      • bacterial
    • Enteritis(acute) (diarrheal) (hemorrhagic) (noninfective)
      • infectious NOS
        • due to
          • bacteria NOS
    • Spondylitis(chronic)
      • in (due to)
        • enterobacteria

Clinical ClassificationClinical

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

CCSR INF003
Bacterial infections
Default principal diagnosis: inpatient No · outpatient No
CCSR DIG001
Intestinal infection
Default principal diagnosis: inpatient Yes · outpatient Yes

Clinical InformationClinical

  • Bacterial Gastroenteritis

    gastroenteritis resulting from a bacterial infection.

Patient EducationClinical

Bacterial Infections

Bacteria are tiny organisms (living things) that have only one cell. Under a microscope, they look like balls, rods, or spirals. They can be found almost everywhere on Earth. There are lots of bacteria in and on your body. In fact, your body has about 10 times more bacteria cells than human cells.

The full article covers:

  • What are bacteria?
  • How do bacterial infections spread?
  • What are the treatments for bacterial infections?
  • Can bacterial infections be prevented?

Read the full article at MedlinePlus

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

Convert A04.9 to ICD-9-CMHistory

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

ICD-9-CM
008.5 Bacterial enteritis NOS
Exact Match The mapping is direct, with no qualifiers.

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 A04.9Overview

Is A04.9 (Other bacterial intestinal infections) a billable code?

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

What MS-DRG does A04.9 group to?

When bacterial intestinal infection, unspecified is the principal diagnosis on an inpatient stay, it groups to MS-DRG 371, 372, 373, with relative weights from 0.7274 to 1.7731 depending on complications. Higher weights mean higher Medicare reimbursement.

What is the ICD-9 equivalent of A04.9?

Under the General Equivalence Mappings, bacterial intestinal infection, unspecified converts to ICD-9-CM 008.5 (bacterial enteritis NOS). The mapping is a direct match.

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.