2027 ICD-10-CM Diagnosis Code A23.9Brucellosis, unspecified

ICD-10-CM Codes›A00–B99›A20-A28›A23

ICD-10-CM A23.9
CMSSource: CMS FY 2027 ICD-10-CM dataset · Effective Oct 1, 2026 – Sep 30, 2027

A23.9 is a billable ICD-10-CM diagnosis code for brucellosis, unspecified. It is valid on HIPAA claims for fiscal year 2027 (October 1, 2026 through September 30, 2027) and groups to MS-DRG 867 through 869. 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 6 closely related codes. Coders also document this condition as brucella infection of the central nervous system. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Bacterial infections.

Code Identity

ICD-10-CM Code
A23.9
Billable Status
Yes — Valid for Submission
Code Describes
Brucellosis, unspecified
Short Description
Brucellosis, unspecified
Same as the full description in the CMS dataset.
Parent Code
A23
Brucellosis

Code Classification

ChapterA00–B99Certain infectious and parasitic diseases
SectionA20-A28Certain zoonotic bacterial diseases
CategoryA23Brucellosis
This CodeA23.9Brucellosis, unspecified

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Brucella infection of the central nervous system
  • Brucella spondylitis
  • Brucellosis
  • Brucellosis of skin
  • Brucellosis uveitis

Instructional NotesGuidance

Instructions from the official ICD-10-CM Tabular List that apply to A23.9: its own notes plus those printed at A23 and 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 A23 Brucellosis applies to 6 codes
  • Malta fever
  • Mediterranean fever
  • undulant fever
From Chapter 1 (A00-B99) Certain infectious and parasitic diseases applies to 1,068 codes
  • diseases generally recognized as communicable or transmissible

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 A23.9, its category, or a range that includes it.

Code First 2

These codes say to code first a condition named in the note, and A23.9 is one of the conditions named.

  • M49 Spondylopathies in diseases classified elsewhere
    brucellosis (A23.-) names A23.-, which includes this code
  • N16 Renal tubulo-interstitial disorders in diseases classified elsewhere
    brucellosis (A23.0-A23.9) names A23.0-A23.9, 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 INF003
Bacterial infections
Default principal diagnosis: inpatient Yes · outpatient Yes

Clinical InformationClinical

  • Brucellosis

    infection caused by bacteria of the genus brucella mainly involving the mononuclear phagocyte system. this condition is characterized by fever, weakness, malaise, and weight loss.

Patient EducationClinical

Animal Diseases and Your Health

Animal diseases that people can catch are called zoonoses. Many diseases affecting humans can be traced to animals or animal products. You can get a disease directly from an animal, or indirectly, through the environment.

Read the full article at MedlinePlus

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

Convert A23.9 to ICD-9-CMHistory

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

ICD-9-CM
023.9 Brucellosis 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 2017–2026No changes
FY 2027CurrentCurrent code set, no changesEffective October 1, 2026 through September 30, 2027.

Questions About A23.9Overview

What is the ICD-10 code for brucellosis, unspecified?

The ICD-10-CM code for brucellosis, unspecified is A23.9 (sometimes written as A239). It is billable on HIPAA-covered claims from October 1, 2026 through September 30, 2027.

Is A23.9 (Brucellosis) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report brucellosis, unspecified on HIPAA-covered claims from October 1, 2026 through September 30, 2027.

What MS-DRG does A23.9 group to?

When brucellosis, unspecified is the principal diagnosis on an inpatient stay, it groups to MS-DRG 867, 869, 868, with relative weights from 0.6784 to 2.1855 depending on complications. Higher weights mean higher Medicare reimbursement.

Is A23.9 a CC or MCC?

CMS lists A23.9 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 6 closely related codes in its exclusion list.

What is the ICD-9 equivalent of A23.9?

Under the General Equivalence Mappings, brucellosis, unspecified converts to ICD-9-CM 023.9 (brucellosis NOS). The mapping is a direct match.