2026 ICD-10-CM Diagnosis Code A48.1Legionnaires' disease
ICD-10-CM Codes›A00–B99›A30-A49›A48
- Billable — Valid for Submission
- MCC — Major Complication or Comorbidity
- Risk Adjusts — HCC 282
- Not Chronic
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, 791, 793, 974 through 976. As a secondary diagnosis, it counts as a major complication or comorbidity (MCC) and places an inpatient stay in the highest severity level of its MS-DRG family. It does not count, however, when the principal diagnosis is one of 129 closely related codes. 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).
For Medicare Advantage risk adjustment, A48.1 maps to CMS-HCC Category 282 (Aspiration and Specified Bacterial Pneumonias) under the V28 model, adding a risk factor of about 0.440 for a community, non-dual, aged beneficiary in payment year 2026.
Code Identity
Code Classification
Medicare Risk Adjustment (HCC)Billing
A48.1 maps to a payment category in the CMS-HCC model used to risk-adjust Medicare Advantage payments. Weights are the published community factors for payment year 2026.
Source: CMS Payment Year 2026 risk adjustment mappings and model software. Weights are relative factors, not dollar amounts; a beneficiary's total RAF also includes demographics and interactions. Browse all CMS-HCC categories.
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.
Disease, diseased See Also: Syndrome;
legionnaires' A48.1
Legionellosis A48.1
Clinical ClassificationClinical
AHRQ’s CCSR groups this code into broader clinical categories.
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.
Code HistoryHistory
Questions About A48.1Overview
What is the ICD-10 code for Legionnaires' disease?
The ICD-10-CM code for Legionnaires' disease is A48.1 (sometimes written as A481). It is billable on HIPAA-covered claims from October 1, 2025 through September 30, 2026.
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, 791, 793, 974, 975, 976, with relative weights from 0.7550 to 4.1696 depending on complications. Higher weights mean higher Medicare reimbursement.
Is A48.1 a CC or MCC?
CMS lists A48.1 as an MCC (major complication or comorbidity) for FY 2026. Reported as a secondary diagnosis, it places the inpatient stay in the highest-weighted DRG of its severity family. It does not count when the principal diagnosis is one of the 129 closely related codes in its exclusion list.
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.
What HCC is A48.1?
A48.1 (Legionnaires' disease) maps to CMS-HCC Category 282 (Aspiration and Specified Bacterial Pneumonias), commonly written as HCC 282, in the CMS-HCC V28 model used for Medicare Advantage risk adjustment in payment year 2026. It mapped to HCC 114 under the retired V24 model. It also maps in the PACE (CMS-HCC V22), ESRD (V21), and ESRD (V24) models. It does not map to any RxHCC in the Part D prescription drug model.
Does A48.1 risk-adjust for Medicare Advantage payment?
Yes. When documented and reported on a Medicare Advantage encounter, A48.1 adds a risk adjustment factor of about 0.440 to the beneficiary's RAF score for a community, non-dual, aged enrollee (published V28 weights range from 0.173 to 0.538 depending on the payment segment). HCC 282 sits at the top of its hierarchy, so no other condition category supersedes it. See the full factor table on the HCC 282 category page.
