2026 ICD-10-CM Diagnosis Code A48.1Legionnaires' disease

ICD-10-CM Codes›A00–B99›A30-A49›A48

ICD-10-CM A48.1
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

A48.1 is a billable ICD-10-CM diagnosis code for Legionnaires' disease. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 177 through 179, 974 through 976. Coders also document this condition as healthcare associated Legionnaires' disease. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Bacterial infections and Pneumonia (except that caused by tuberculosis).

Code Identity

ICD-10-CM Code
A48.1
Billable Status
Yes — Valid for Submission
Code Describes
Legionnaires' disease
Short Description
Legionnaires' disease
Same as the full description in the CMS dataset.
Parent Code
A48
Other bacterial diseases, not elsewhere classified

Code Classification

ChapterA00–B99Certain infectious and parasitic diseases
SectionA30-A49Other bacterial diseases
CategoryA48Other bacterial diseases, not elsewhere classified
This CodeA48.1Legionnaires' disease

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Healthcare associated Legionnaires' disease
  • Infection by Legionella pneumophilia
  • Interstitial pneumonia
  • Legionella infection
  • Legionella pneumonia
  • Pittsburgh pneumonia

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
      • legionnaires'
    • Infection, infected, infective(opportunistic)
      • Legionella pneumophila
    • Legionellosis
    • Legionnaires'
      • disease
    • Legionnaires'
      • pneumonia

Clinical ClassificationClinical

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

CCSR INF003
Bacterial infections
Default principal diagnosis: inpatient No · outpatient No
CCSR RSP002
Pneumonia (except that caused by tuberculosis)
Default principal diagnosis: inpatient Yes · outpatient Yes

Clinical InformationClinical

  • Legionnaires' Disease

    an acute, sometimes fatal, pneumonia-like bacterial infection characterized by high fever, malaise, muscle aches, respiratory disorders and headache. it is named for an outbreak at the 1976 philadelphia convention of the american legion.

Patient EducationClinical

Legionnaires' Disease

Legionnaires' disease is a serious type of pneumonia caused by Legionella bacteria. The disease got its name when a group of people at an American Legion convention became ill with this type of pneumonia.

The full article covers:

  • What is Legionnaires' Disease?
  • What causes Legionnaires' disease?
  • Who is more likely to develop Legionnaires' disease?
  • What are the symptoms of Legionnaires' disease?
  • What other problems can Legionnaires' disease cause?
  • How is Legionnaires' disease diagnosed?
  • What are the treatments for Legionnaires' disease?
  • Can Legionnaires' disease be prevented?

Read the full article at MedlinePlus

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

Convert A48.1 to ICD-9-CMHistory

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

ICD-9-CM
482.84 Legionnaires' disease
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 A48.1Overview

Is A48.1 (Other bacterial diseases, not elsewhere classified) a billable code?

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

What MS-DRG does A48.1 group to?

When Legionnaires' disease is the principal diagnosis on an inpatient stay, it groups to MS-DRG 177, 178, 179, 974, 975, 976, with relative weights from 0.7550 to 2.8860 depending on complications. Higher weights mean higher Medicare reimbursement.

What is the ICD-9 equivalent of A48.1?

Under the General Equivalence Mappings, Legionnaires' disease converts to ICD-9-CM 482.84 (Legionnaires' disease). 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.