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A83.2 ICD-10-CM Code: Eastern equine encephalitis

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

Coding at a Glance

Tabular directives
1 inclusion term · 3 Excludes1 · 3 Excludes2

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 023 — CRANIOTOMY WITH MAJOR DEVICE IMPLANT OR ACUTE COMPLEX CNS PRINCIPAL DIAGNOSIS WITH MCC OR ANTINEOPLASTIC IMPLANT OR EPILEPSY WITH NEUROSTIMULATOR (MDC 01)
  • MS-DRG 024 — CRANIOTOMY WITH MAJOR DEVICE IMPLANT OR ACUTE COMPLEX CNS PRINCIPAL DIAGNOSIS WITHOUT MCC (MDC 01)
  • MS-DRG 097 — NON-BACTERIAL INFECTION OF NERVOUS SYSTEM EXCEPT VIRAL MENINGITIS WITH MCC (MDC 01)
  • MS-DRG 098 — NON-BACTERIAL INFECTION OF NERVOUS SYSTEM EXCEPT VIRAL MENINGITIS WITH CC (MDC 01)
  • MS-DRG 099 — NON-BACTERIAL INFECTION OF NERVOUS SYSTEM EXCEPT VIRAL MENINGITIS WITHOUT CC/MCC (MDC 01)

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.

Coding instructions

Official Tabular Instructional Notes: the inclusion, exclusion and sequencing notes published for A83.2 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 A83.2 itself; “inherited from” names the category or block whose note applies here.

Includes

Conditions the official ICD-10-CM tabular list includes under this code.

  • mosquito-borne viral meningoencephalitis

Source: inherited from A83

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 A80-A89

Excludes2 — Not Included Here

Conditions not covered by this code, but which may be reported alongside it when both are present.

Source: inherited from A83

Coder workflow for A83.2

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

Before you code A83.2

  1. Check the Excludes1 note: if the documentation supports a condition named there, do not simply proceed with A83.2. 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 A83.2’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.

    ReviewG14, B91, B94.1

Consider A83.2. 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 A83.2(3 notes)

    Coding workflow: If the documentation supports a condition named in this note, do not simply proceed with A83.2: the two are not reported together. The one exception is when the record shows the two conditions are unrelated to each other.

    CompareG14, B91, B94.1

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

  • Excludes2 — not part of A83.2(3 notes)

    Coding workflow: The conditions named in this note are not included in A83.2. When the record documents both, both may be reported; the note is a boundary, not a prohibition.

    CompareA92.2, A92.3

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

Coding decision scenarios

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

Documentation: Both the condition A83.2 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).

ReviewG14, B91, B94.1

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

Eastern equine encephalitis is a billable ICD-10-CM diagnosis code (A83.2).

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 (4)

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

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 174 clinically related codes on its CMS exclusion list.

Named in the grouper logic of 5 MS-DRGs: DRG 023 (MDC 01), DRG 024 (MDC 01), DRG 097 (MDC 01), DRG 098 (MDC 01), DRG 099 (MDC 01).

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

Clinical classification (AHRQ CCSR):NVS002 — Encephalitis (default); INF008 — Viral infection.

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.

A50.42 — Late congenital syphilitic encephalitis, A52.14 — Late syphilitic encephalitis, A75.9 — Typhus fever, unspecified, A79.9 — Rickettsiosis, unspecified, A81.1 — Subacute sclerosing panencephalitis, A81.82 — Gerstmann-Sträussler-Scheinker syndrome, A81.83 — Fatal familial insomnia, A81.89 — Other atypical virus infections of central nervous system, A83.0 — Japanese encephalitis, A83.1 — Western equine encephalitis, A83.3 — St Louis encephalitis, A83.4 — Australian encephalitis, A83.5 — California encephalitis, A83.6 — Rocio virus disease, A83.8 — Other mosquito-borne viral encephalitis, A83.9 — Mosquito-borne viral encephalitis, unspecified, A84.0 — Far Eastern tick-borne encephalitis [Russian spring-summer encephalitis], A84.1 — Central European tick-borne encephalitis, A84.81 — Powassan virus disease, A84.89 — Other tick-borne viral encephalitis, +153 more

Same clinical category (CCSR)

AHRQ's Clinical Classifications Software groups these diagnoses under the same clinical categories (Encephalitis, Viral infection).

A17.82 — Tuberculous meningoencephalitis, A32.12 — Listerial meningoencephalitis, A39.81 — Meningococcal encephalitis, A42.82 — Actinomycotic encephalitis, A50.42 — Late congenital syphilitic encephalitis, A52.14 — Late syphilitic encephalitis, A81.1 — Subacute sclerosing panencephalitis, A83.0 — Japanese encephalitis, A83.1 — Western equine encephalitis, A83.3 — St Louis encephalitis, A83.4 — Australian encephalitis, A83.5 — California encephalitis, A83.6 — Rocio virus disease, A83.8 — Other mosquito-borne viral encephalitis, A83.9 — Mosquito-borne viral encephalitis, unspecified, A84.0 — Far Eastern tick-borne encephalitis [Russian spring-summer encephalitis], A84.1 — Central European tick-borne encephalitis, A84.8 — Other tick-borne viral encephalitis, A84.81 — Powassan virus disease, A84.89 — Other tick-borne viral encephalitis, +314 more

Same Index main term, other category

The ICD-10-CM Index to Diseases and Injuries files this code under the main term “Encephalitis”; these codes share that main term but sit in a different category of the Tabular List.

A17.82 — Tuberculous meningoencephalitis (in, tuberculosis), A28.1 — Cat-scratch disease (due to, cat scratch disease), A32.12 — Listerial meningoencephalitis (in, listeriosis), A39.81 — Meningococcal encephalitis (meningococcal), A42.82 — Actinomycotic encephalitis (in, actinomycosis), A50.42 — Late congenital syphilitic encephalitis (in, syphilis, congenital), A52.14 — Late syphilitic encephalitis (in, syphilis, late), A80.9 — Acute poliomyelitis, unspecified (in, poliovirus), A81.1 — Subacute sclerosing panencephalitis (Dawson's), A84.0 — Far Eastern tick-borne encephalitis [Russian spring-summer encephalitis] (Far Eastern), A84.1 — Central European tick-borne encephalitis (Czechoslovakian), A84.81 — Powassan virus disease (Powassan), A84.89 — Other tick-borne viral encephalitis (louping ill), A84.9 — Tick-borne viral encephalitis, unspecified (tick-borne), A85.0 — Enteroviral encephalitis (in, enterovirus), A85.1 — Adenoviral encephalitis (in, adenovirus), A85.2 — Arthropod-borne viral encephalitis, unspecified (arthropod-borne NEC), A85.8 — Other specified viral encephalitis (Mengo), A86 — Unspecified viral encephalitis (acute), A87.2 — Lymphocytic choriomeningitis (lymphatica), +38 more

Contextual Map

Every relationship of A83.2 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.

Hierarchy

Clinical classification (CCSR)

MS-DRG Grouper

MDC crossing

  • MDC 01 — Diseases and Disorders of the Nervous System[MDC crossing]: “Diseases and Disorders of the Nervous 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. 8,892 same-MDC procedures group here; browse them on the MDC page.”— CMS MS-DRG Definitions Manual · FY2026

Index entries

  • Encephalitis (chronic) (hemorrhagic) (idiopathic) (nonepidemic) (spurious) (subacute), Eastern equine[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2026
  • Encephalitis (chronic) (hemorrhagic) (idiopathic) (nonepidemic) (spurious) (subacute), equine (acute) (infectious) (viral), Eastern[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2026
  • Encephalitis (chronic) (hemorrhagic) (idiopathic) (nonepidemic) (spurious) (subacute), viral, virus, arthropod-borne NEC, mosquito-borne, Eastern equine[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2026
  • Encephalomyelitis, equine, Eastern[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
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. "A83.2 — Eastern equine encephalitis." ICD-10-CM FY2026. https://medcoder.ai/icd10/code/a83.2-eastern-equine-encephalitis

Change history

  • FY2016 — October 1, 2015
    In the code set at ICD-10-CM adoption
    Eastern equine encephalitis

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 A83.2 in its code family, with their registry titles.

View all codes in the A83 family