2026 ICD-10-CM Diagnosis Code A92.31West Nile virus infection with encephalitis

ICD-10-CM Codes›A00–B99›A90-A99›A92

ICD-10-CM A92.31
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

A92.31 is a billable ICD-10-CM diagnosis code for West Nile virus infection with encephalitis. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 865 through 866. Coders also document this condition as disease caused by West Nile virus. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Encephalitis and Viral infection.

Code Identity

ICD-10-CM Code
A92.31
Billable Status
Yes — Valid for Submission
Code Describes
West Nile virus infection with encephalitis
Short Description
West Nile virus infection with encephalitis
Same as the full description in the CMS dataset.
Parent Code
A92.3
West Nile virus infection

Code Classification

ChapterA00–B99Certain infectious and parasitic diseases
SectionA90-A99Arthropod-borne viral fevers and viral hemorrhagic fevers
CategoryA92Other mosquito-borne viral fevers
This CodeA92.31West Nile virus infection with encephalitis

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Disease caused by West Nile virus
  • Disorder of nervous system caused by West Nile virus
  • West Nile encephalitis

Tabular List NotesGuidance

Coding notes and annotation back-references applicable to this code.

Inclusion Terms

  • West Nile encephalitis
  • West Nile encephalomyelitis

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.

    • Fever(inanition) (of unknown origin) (persistent) (with chills) (with rigor)
      • West
        • Nile (viral)
          • with
            • encephalitis
    • Fever(inanition) (of unknown origin) (persistent) (with chills) (with rigor)
      • West
        • Nile (viral)
          • with
            • encephalomyelitis
    • Virus, viral
      • West Nile (fever)
        • with
          • encephalitis
    • Virus, viral
      • West Nile (fever)
        • with
          • encephalomyelitis

Clinical ClassificationClinical

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

CCSR NVS002
Encephalitis
Default principal diagnosis: inpatient No · outpatient No
CCSR INF008
Viral infection
Default principal diagnosis: inpatient Yes · outpatient Yes

Patient EducationClinical

Encephalitis

Encephalitis is inflammation (swelling) of the brain. It can happen when an infection or medical condition that affects the brain activates your immune system. The inflammation can cause a wide range of symptoms. In extreme cases, it can lead to brain damage, stroke, or even death.

The full article covers:

  • What is encephalitis?
  • What causes encephalitis?
  • Who is more likely to get encephalitis?
  • What are the symptoms of encephalitis?
  • How is encephalitis diagnosed?
  • What are the treatments for encephalitis?
  • Can encephalitis be prevented?

Read the full article at MedlinePlus

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

Convert A92.31 to ICD-9-CMHistory

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

ICD-9-CM
066.41 West Nile Fever w/enceph
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 A92.31Overview

Is A92.31 (West Nile virus infection) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report West Nile virus infection with encephalitis on HIPAA-covered claims from October 1, 2025 through September 30, 2026.

What MS-DRG does A92.31 group to?

When West Nile virus infection with encephalitis is the principal diagnosis on an inpatient stay, it groups to MS-DRG 865, 866, with relative weights from 0.8696 to 1.4983 depending on complications. Higher weights mean higher Medicare reimbursement.

What is the ICD-9 equivalent of A92.31?

Under the General Equivalence Mappings, West Nile virus infection with encephalitis converts to ICD-9-CM 066.41 (West Nile Fever w/enceph). 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.