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A48.1 ICD-10-CM Code: Legionnaires' disease

Billing Status: YES. This is a valid, specific, and billable ICD-10-CM reference.

Coding at a Glance

Tabular directives
1 Excludes1
Risk adjustment
CMS-HCC V28: 1 category · CMS-HCC V22 category 114

Inpatient Payment Groups (MS-DRG)

Potential MS-DRG participation — not a DRG assignment.

MS-DRGs this diagnosis helps define, as principal or secondary, per the CMS ICD-10-CM/PCS MS-DRG Definitions Manual v43, Appendix B.

  • MS-DRG 177 — RESPIRATORY INFECTIONS AND INFLAMMATIONS WITH MCC (MDC 04)
  • MS-DRG 178 — RESPIRATORY INFECTIONS AND INFLAMMATIONS WITH CC (MDC 04)
  • MS-DRG 179 — RESPIRATORY INFECTIONS AND INFLAMMATIONS WITHOUT CC/MCC (MDC 04)
  • MS-DRG 791 — PREMATURITY WITH MAJOR PROBLEMS (MDC 15)
  • MS-DRG 793 — FULL TERM NEONATE WITH MAJOR PROBLEMS (MDC 15)
  • MS-DRG 974 — HIV WITH MAJOR RELATED CONDITION WITH MCC (MDC 25)
  • MS-DRG 975 — HIV WITH MAJOR RELATED CONDITION WITH CC (MDC 25)
  • MS-DRG 976 — HIV WITH MAJOR RELATED CONDITION WITHOUT CC/MCC (MDC 25)

A diagnosis appearing in a group's logic does not by itself determine the DRG assigned to a stay; the grouper uses the full claim.

Risk Adjustment (CMS-HCC)

Payment categories this diagnosis maps to under CMS-HCC V28, payment year 2026.

  • HCC 282 — Aspiration and Specified Bacterial Pneumonias (supersedes HCC 283)

Other models: CMS-HCC V22 HCC 114

Risk scores depend on the enrollee's full accepted diagnosis set and segment; a category mapping alone does not determine payment.

Coding instructions

Official Tabular Instructional Notes: the inclusion, exclusion and sequencing notes published for A48.1 in the official ICD-10-CM tabular list, quoted as published.

Source: CMS/CDC — ICD-10-CM Tabular ListRelease: FY2026Effective: October 1, 2025

Notes without a marker are published on A48.1 itself; “inherited from” names the category or block whose note applies here.

Excludes1 — Not Coded Here

Conditions generally not reported together with this code (Excludes1) -- an error unless the two conditions are documented as unrelated to each other (ICD-10-CM Official Guidelines, Section I.A.12.a).

Source: inherited from A48

Coder workflow for A48.1

MedCoder structured workflow — derived from this code’s own official record

Before you code A48.1

  1. Check the Excludes1 note: if the documentation supports a condition named there, do not simply proceed with A48.1. Excludes1 conditions are not reported together with this code unless the record shows they are unrelated (Guidelines I.A.12.a).

    See the official tabular notes

Choose the right path

  1. Does the documentation support a condition named in A48.1’s Excludes1 note?
    Yes → Do not simply proceed: review the excluded code. Both are reported only when the record shows the two conditions are unrelated.
    No → Continue.

    ReviewB47.1

Consider A48.1. Then confirm the code is valid for the date of service in the Verify section.

Documentation check

The provider’s diagnostic statement
Codes are assigned from the provider’s documented diagnosis, not from clinical criteria, test values or a medication list (Guidelines I.A.19).

Official instructions as workflow

  • Excludes1 — check before selecting A48.1(1 note)

    Coding workflow: If the documentation supports a condition named in this note, do not simply proceed with A48.1: the two are not reported together. The one exception is when the record shows the two conditions are unrelated to each other.

    CompareB47.1

    See the official tabular notes · Guidelines I.A.12.a

Coding decision scenarios

Pattern scenarios for this code’s structure — decision rules, not clinical cases

Documentation: Both the condition A48.1 describes and a condition named in its Excludes1 note are documented for the same encounter.

Coding question: Can both codes be reported?

Path: Review the Excludes1 note and the excluded code, and look for a provider statement on whether the two conditions are related.

Reason: Excludes1 means the two are not coded together; the exception is when the record shows the conditions are unrelated to each other (Guidelines I.A.12.a).

ReviewB47.1

Every row is derived from this code’s own record — its title, tabular notes, 7th-character family and same-category siblings — with fixed MedCoder wording; nothing is inferred about a patient. The official notes and guideline text are in the sections each row links to, and they control.

Code Overview

Legionnaires' disease is a billable ICD-10-CM diagnosis code (A48.1).

MedCoder summary Summary composed by MedCoder from this code's official ICD-10-CM record. The tabular instructional notes themselves appear verbatim below.

Indexed Clinical Terms (5)

Official source data — entries quoted as published, in the Index’s own lookup phrasing

Clinical term phrases from the official ICD-10-CM Index to Diseases and Injuries that map to this code. These are alphabetic-index entries shown as the Index writes them — lookup phrasing, not necessarily the wording of a final diagnosis.

Verify Before Coding

  • MCC as a secondary diagnosis (FY2026). Can raise the stay's MS-DRG severity tier.

From the code registry, the Medicare Code Editor, and the MS-DRG Definitions Manual. Check it against a full claim in Claim Check.

Relationships & Classification

MedCoder structured relationships — computed from published CMS and AHRQ datasets

Other codes that name A48.1 or its code family, from the CMS ICD-10-CM tabular instructional notes. Tabular-note edges are stored at the code family level that carries each note.

Referenced by 1 Excludes1 note: J15 — Bacterial pneumonia, not elsewhere classified.

These codes’ tabular lists mark this diagnosis as mutually exclusive — not reported together unless the conditions are documented as unrelated.

MS-DRG Grouper Relationships (FY2026)

Potential MS-DRG participation — not a DRG assignment.

FY2026 MS-DRG: MCC — Major Complication or Comorbidity. Reported as a secondary diagnosis, this code raises the stay's MS-DRG severity tier — except when the principal diagnosis is one of 129 clinically related codes on its CMS exclusion list. Does not count toward severity when the stay groups to DRGs 177-179 (Respiratory Infections and Inflammations); DRGs 974-976 (HIV with Major Related Condition).

Named in the grouper logic of 8 MS-DRGs: DRG 177 (MDC 04), DRG 178 (MDC 04), DRG 179 (MDC 04), DRG 791 (MDC 15), DRG 793 (MDC 15), DRG 974 (MDC 25), DRG 975 (MDC 25), DRG 976 (MDC 25).

From the CMS MS-DRG Definitions Manual (Appendices B and C). Actual DRG assignment depends on the complete claim.

Clinical classification (AHRQ CCSR):RSP002 — Pneumonia (except that caused by tuberculosis) (default); INF003 — Bacterial infections.

Clinical Classifications Software Refined (CCSR) for ICD-10-CM Diagnoses. Healthcare Cost and Utilization Project (HCUP), Agency for Healthcare Research and Quality.

Related Codes

Same clinical process (MS-DRG)

Acts as MCC — raises the severity of other admissions. CMS groups these diagnoses into one MS-DRG principal-diagnosis exclusion process — a CC/MCC on this list never raises severity when the principal diagnosis is also on it.

A18.89 — Tuberculosis of other sites, A21.2 — Pulmonary tularemia, A22.1 — Pulmonary anthrax, A31.0 — Pulmonary mycobacterial infection, A37.01 — Whooping cough due to Bordetella pertussis with pneumonia, A37.11 — Whooping cough due to Bordetella parapertussis with pneumonia, A37.81 — Whooping cough due to other Bordetella species with pneumonia, A37.91 — Whooping cough, unspecified species with pneumonia, A42.0 — Pulmonary actinomycosis, A43.0 — Pulmonary nocardiosis, B25.0 — Cytomegaloviral pneumonitis, B39.0 — Acute pulmonary histoplasmosis capsulati, B39.1 — Chronic pulmonary histoplasmosis capsulati, B39.2 — Pulmonary histoplasmosis capsulati, unspecified, B44.0 — Invasive pulmonary aspergillosis, B58.3 — Pulmonary toxoplasmosis, B59 — Pneumocystosis, B67.1 — Echinococcus granulosus infection of lung, J09.X1 — Influenza due to identified novel influenza A virus with pneumonia, J09.X2 — Influenza due to identified novel influenza A virus with other respiratory manifestations, +108 more

Same CMS-HCC risk category (V28)

CMS maps these diagnoses to the same Hierarchical Condition Category (Aspiration and Specified Bacterial Pneumonias) for risk-adjusted payment.

J15.0 — Pneumonia due to Klebsiella pneumoniae, J15.1 — Pneumonia due to Pseudomonas, J15.20 — Pneumonia due to staphylococcus, unspecified, J15.211 — Pneumonia due to Methicillin susceptible Staphylococcus aureus, J15.212 — Pneumonia due to Methicillin resistant Staphylococcus aureus, J15.29 — Pneumonia due to other staphylococcus, J15.5 — Pneumonia due to Escherichia coli, J15.61 — Pneumonia due to Acinetobacter baumannii, J15.69 — Pneumonia due to other Gram-negative bacteria, J15.8 — Pneumonia due to other specified bacteria, J69.0 — Pneumonitis due to inhalation of food and vomit, J69.1 — Pneumonitis due to inhalation of oils and essences, J69.8 — Pneumonitis due to inhalation of other solids and liquids

Related risk categories

These categories interact through CMS's HCC hierarchy — one can suppress the other's risk-adjustment weight when both are present on a claim.

Empyema, Lung Abscess

Same clinical category (CCSR)

AHRQ's Clinical Classifications Software groups these diagnoses under the same clinical categories (Pneumonia (except that caused by tuberculosis), Bacterial infections).

A02.22 — Salmonella pneumonia, A20.2 — Pneumonic plague, A21.2 — Pulmonary tularemia, A22.1 — Pulmonary anthrax, A31.0 — Pulmonary mycobacterial infection, A37.01 — Whooping cough due to Bordetella pertussis with pneumonia, A37.11 — Whooping cough due to Bordetella parapertussis with pneumonia, A37.81 — Whooping cough due to other Bordetella species with pneumonia, A37.91 — Whooping cough, unspecified species with pneumonia, A43.0 — Pulmonary nocardiosis, A50.04 — Early congenital syphilitic pneumonia, A52.72 — Syphilis of lung and bronchus, A54.84 — Gonococcal pneumonia, B01.2 — Varicella pneumonia, B05.2 — Measles complicated by pneumonia, B06.81 — Rubella pneumonia, B25.0 — Cytomegaloviral pneumonitis, B37.1 — Pulmonary candidiasis, B38.0 — Acute pulmonary coccidioidomycosis, B38.1 — Chronic pulmonary coccidioidomycosis, +418 more

Lab tests where this diagnosis supports Medicare coverage (NCD)

Medicare's National Coverage Determination (NCD) program lists this diagnosis as medical justification for these lab tests.

Blood Glucose Test, HIV Screening Test

Contextual Map

Every relationship of A48.1 in one view: hierarchy, official tabular instructions in both directions, clinical classification, risk adjustment, MS-DRG participation, index terms and change history — each edge carrying the CMS source it derives from.

Run A48.1 with this related code in Claim Check

Hierarchy

Referenced by Excludes1 notes

Clinical classification (CCSR)

Risk adjustment (CMS-HCC)

  • HCC 282 — Aspiration and Specified Bacterial Pneumonias [CMS-HCC]: “Aspiration and Specified Bacterial Pneumonias — supersedes HCC 283 (Empyema, Lung Abscess)”— CMS-HCC V28 · 2026

MS-DRG Grouper

MDC crossing

  • MDC 04 — Diseases and Disorders of the Respiratory System[MDC crossing]: “Diseases and Disorders of the Respiratory System — the grouper's crossing between diagnoses and procedures: a principal diagnosis sets the MDC, and same-MDC procedures move the stay to its surgical DRGs. 3,998 same-MDC procedures group here; browse them on the MDC page.”— CMS MS-DRG Definitions Manual · FY2026
  • MDC 15 — Newborns and Other Neonates with Conditions Originating in Perinatal Period[MDC crossing]: “Newborns and Other Neonates with Conditions Originating in Perinatal Period — the grouper's crossing between diagnoses and procedures: a principal diagnosis sets the MDC, and same-MDC procedures move the stay to its surgical DRGs.”— CMS MS-DRG Definitions Manual · FY2026

Index entries

  • Disease, diseased, legionnaires'[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2026
  • Infection, infected, infective (opportunistic), Legionella pneumophila[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2026
  • Legionellosis[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2026
  • Legionnaires', disease[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2026
  • Legionnaires', pneumonia[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2026

Nearest codes (9)

Change history

  • FY2016 — In the code set at ICD-10-CM adoption [Change history]— CMS release files (code change ledger) · icd10cm-fy2016

Sources for this page

Codes, titles, notes, index terms and mappings on this page are transcribed from the datasets below. Relationships MedCoder computed and text MedCoder wrote are labelled where they appear.

Code, title, tabular notes and index terms Official source data
CMS/CDC ICD-10-CM FY2026 tabular list, index and tables, effective October 1, 2025 Release, file and checksum · Publisher’s page
Claim edits Official source data
CMS Definitions of Medicare Code Edits — v43.1 (April 2026) Release, file and checksum · Publisher’s page
Inpatient payment groups Official source data
CMS MS-DRG Definitions Manual (incl. Appendix B diagnosis index, Appendix C CC/MCC list, Appendix E procedure index) and IPPS Final Rule tables — v43 Release, file and checksum · Publisher’s page
Risk adjustment Official source data
2026 Mid-Year Final ICD-10 Mappings + Model Software (cms.gov/files/zip/2026-midyear-final-icd-10-mappings.zip, 2026-midyear-final-model-software.zip) — CMS-HCC V28, PY2026 mid-year final release Release, file and checksum · Publisher’s page
Change history and date-of-service validity Official source data
CMS ICD-10-CM release addenda, ingested release by release into the change ledger Release, file and checksum · Publisher’s page
Comparisons, relationships and the contextual map MedCoder structured relationship
Computed by MedCoder from the tabular notes and tables above; every derived relationship is marked as derived where it appears
Summary and FAQ answers MedCoder explanation
Written by MedCoder to explain the sources above: drafted with AI assistance, checked by a person against the release files, and labelled as MedCoder text where it appears. Not official text.

Labels on this page: Official source data · MedCoder structured relationship · MedCoder explanation. How to read the labels · All data sources and release dates

Cite this page

Reference this page in a research guide, syllabus or article. The release is included because code content changes each year.

MedCoder.ai. "A48.1 — Legionnaires' disease." ICD-10-CM FY2026. https://medcoder.ai/icd10/code/a48.1-legionnaires-disease

Change history

  • FY2016 — October 1, 2015
    In the code set at ICD-10-CM adoption
    Legionnaires' disease

No changes since FY2016 — additions, deletions, description changes and billable-status changes are tracked through FY2027 (effective October 1, 2026), and none are recorded for this code. Note changes are tracked from FY2027 only.

Nearest Codes in This Family

Official ICD-10-CM classifications closest to A48.1 in its code family, with their registry titles.

View all codes in the A48 family