2026 ICD-10-CM Diagnosis Code A31.9Mycobacterial infection, unspecified

ICD-10-CM Codes›A00–B99›A30-A49›A31

ICD-10-CM A31.9
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

A31.9 is a billable ICD-10-CM diagnosis code for mycobacterial infection, unspecified. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 867 through 869, 974 through 976. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Bacterial infections.

Code Identity

ICD-10-CM Code
A31.9
Billable Status
Yes — Valid for Submission
Code Describes
Mycobacterial infection, unspecified
Short Description
Mycobacterial infection, unspecified
Same as the full description in the CMS dataset.
Parent Code
A31
Infection due to other mycobacteria

Code Classification

ChapterA00–B99Certain infectious and parasitic diseases
SectionA30-A49Other bacterial diseases
CategoryA31Infection due to other mycobacteria
This CodeA31.9Mycobacterial infection, unspecified

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Abscess of spinal cord caused by bacterium
  • Abscess of spinal epidural space caused by bacterium
  • Abscess of spinal epidural space caused by Mycobacterium
  • Acid-fast bacteria present
  • Arthropathy associated with bacterial disease
  • Atypical mycobacterial infection
  • Atypical mycobacterial infection of hand
  • Disseminated atypical infection caused by Mycobacterium co-occurrent with human immunodeficiency virus infection
  • Disseminated atypical mycobacterial infection
  • Disseminated mycobacteriosis
  • Granuloma of spinal cord caused by bacterium
  • Granuloma of spinal cord caused by Mycobacterium
  • Infection caused by Mycobacterium resistant to multiple antimycobacterial agents
  • Infection caused by Mycobacteroides abscessus
  • Mycobacterial gastritis
  • Mycobacterial infection
  • Mycobacterial infection of the central nervous system
  • Mycobacterial postinfective arthritis
  • Mycobacterial spinal cord abscess
  • Mycobacteriosis
  • Mycobacteriosis with AIDS
  • Post-bacterial arthropathy
  • Reactive arthritis due to and following mycobacteriosis
  • Skin and soft tissue atypical mycobacterial infection
  • Spinal epidural abscess

Tabular List NotesGuidance

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

Inclusion Terms

  • Atypical mycobacterial infection NOS
  • Mycobacteriosis 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.

    • Disease, diseased
      • photochromogenic (acid-fast bacilli) (pulmonary)
        • nonpulmonary
    • Mycobacterium, mycobacterial(infection)
    • Mycobacterium, mycobacterial(infection)
      • anonymous
    • Mycobacterium, mycobacterial(infection)
      • atypical

Clinical ClassificationClinical

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

CCSR INF003
Bacterial infections
Default principal diagnosis: inpatient Yes · outpatient Yes

Patient EducationClinical

Mycobacterial Infections

Mycobacteria are a type of germ. There are many different kinds. The most common one causes tuberculosis. Another one causes leprosy. Still others cause infections that are called atypical mycobacterial infections. They aren't "typical" because they don't cause tuberculosis.

Read the full article at MedlinePlus

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

Convert A31.9 to ICD-9-CMHistory

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

ICD-9-CM
031.9 Mycobacterial dis 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 A31.9Overview

Is A31.9 (Infection due to other mycobacteria) a billable code?

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

What MS-DRG does A31.9 group to?

When mycobacterial infection, unspecified is the principal diagnosis on an inpatient stay, it groups to MS-DRG 867, 868, 869, 974, 975, 976, with relative weights from 0.7297 to 2.8860 depending on complications. Higher weights mean higher Medicare reimbursement.

What is the ICD-9 equivalent of A31.9?

Under the General Equivalence Mappings, mycobacterial infection, unspecified converts to ICD-9-CM 031.9 (mycobacterial dis 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.