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    OpenPayerBilling CodesViral and prion infections of the central nervous systemICD-10-CM a83-mosquito-borne-viral-encephalitis
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    ICD-10-CM Code For Mosquito-Borne Viral Encephalitis: Group Overview

    The International Classification of Diseases, Tenth Revision, Clinical Modification (ICD-10-CM) code group A83 includes encephalitis caused by mosquito-borne viruses such as West Nile virus and other arthropod-transmitted viral infections that involve the central nervous system. These ICD-10-CM diagnosis codes are used to document clinical presentations of viral encephalitis, capturing severity, neurologic involvement, and complications such as seizures or focal deficits. Accurate coding within the ICD-10-CM A83 group supports proper claim adjudication and complete clinical documentation for appropriate reimbursement.

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    ICD-10-CM A83: Mosquito-Borne Viral Encephalitis Overview

    The ICD-10-CM A83 diagnoses represent encephalitis caused by mosquito-borne viruses affecting the central nervous system. These conditions target the brain and meninges and can cause altered mental status, seizures, and focal neurologic deficits. Accurate coding is important for clinical documentation, public health surveillance, and appropriate reimbursement for the intensity of care provided.

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    When to Use

    Use a code from this group when clinical, laboratory, or epidemiologic evidence supports encephalitis attributable to a mosquito-borne viral agent. Select the most specific code available for the identified virus or use the unspecified mosquito-borne viral encephalitis code when the causative agent is not determined.

    ICD-10-CM Codes

    9 rows

    ICD-10-CM CodeDescription
    A83.0Japanese encephalitis
    A83.1Western equine encephalitis
    A83.2Eastern equine encephalitis
    A83.3St Louis encephalitis
    A83.4Australian encephalitis
    A83.5California encephalitis
    A83.6Rocio virus disease
    A83.8Other mosquito-borne viral encephalitis
    A83.9Mosquito-borne viral encephalitis, unspecified

    DRG Codes

    5 rows

    DRG CodeDescription
    023Craniotomy with Major Device Implant or Acute Complex CNS Principal Diagnosis with MCC or Antineoplastic Implant or Epilepsy with Neurostimulator
    024Craniotomy with Major Device Implant or Acute Complex CNS Principal Diagnosis without MCC
    097Non-Bacterial Infection of Nervous System Except Viral Meningitis with MCC
    098Non-Bacterial Infection of Nervous System Except Viral Meningitis with CC
    099Non-Bacterial Infection of Nervous System Except Viral Meningitis without CC/MCC

    Typical Clinical Scenarios

    • An adult presents to the emergency department with acute high fever, severe headache, photophobia, neck stiffness, confusion, and new-onset focal neurologic deficits after recent travel to a region with active mosquito-borne virus transmission. Cerebrospinal fluid shows lymphocytic pleocytosis and elevated protein, and PCR testing identifies West Nile virus as the etiologic agent; hospitalization and neurologic monitoring are required, so a mosquito-borne viral encephalitis diagnosis is assigned. Typical codes: A83.1, A83.2
    • An elderly nursing home resident with progressive lethargy and altered mental status over several days develops seizures and decreased responsiveness following a documented mosquito-borne viral infection during the local outbreak season. Neuroimaging and CSF studies support viral encephalitis as the cause of the acute decline, and the condition is coded as mosquito-borne viral encephalitis as the principal reason for admission and care. Typical codes: A83.0, A83.5
    • A pediatric patient is evaluated in outpatient infectious disease clinic weeks after hospitalization for acute encephalitis; they have persistent cognitive deficits and motor weakness attributed to prior mosquito-transmitted viral encephalitis. The visit documents sequelae and ongoing rehabilitation needs related to the prior infection, so a post-encephalitic diagnosis from this group is used in the record. Typical codes: A83.8, A83.9

    Related Codes

    A80-ACUTE-POLIOMYELITIS

    ICD-10-CM Code For Acute Poliomyelitis: Group Overview

    A81-ATYPICAL-VIRUS-INFECTIONS-CENTRAL-NERVOUS-SYSTEM

    ICD-10-CM Code For Atypical Virus Infections Of Central Nervous System: Group Overview

    A82-RABIES

    ICD-10-CM Code For Rabies: Group Overview

    A84-TICK-BORNE-VIRAL-ENCEPHALITIS

    ICD-10-CM Code For Tick-Borne Viral Encephalitis: Group Overview

    A85-OTHER-VIRAL-ENCEPHALITIS

    ICD-10-CM Code For Other Viral Encephalitis Not Elsewhere Classified: Group Overview

    A86-UNSPECIFIED-VIRAL-ENCEPHALITIS

    ICD-10-CM Code For Unspecified Viral Encephalitis: Group Overview

    A87-VIRAL-MENINGITIS

    ICD-10-CM Code For Viral Meningitis: Group Overview

    A88-OTHER-VIRAL-CENTRAL-NERVOUS-SYSTEM-INFECTIONS

    ICD-10-CM Code For Other Viral Infections Of Central Nervous System Not Elsewhere Classified: Group Overview

    A89-UNSPECIFIED-VIRAL-INFECTION-CENTRAL-NERVOUS-SYSTEM

    ICD-10-CM Code For Unspecified Viral Infection Of Central Nervous System: Group Overview

    Frequently Asked Questions

    References

    1. 1.CPT® Codes and Descriptions. AAPC. Retrieved Aug 11, 2026.Maintains the CPT code set's official descriptions and guidelines, licensed from the American Medical Association, used as the definitional source for CPT codes on this page.
    2. 2.HCPCS Quarterly Update. Centers for Medicare & Medicaid Services (CMS). Retrieved Aug 11, 2026.CMS's quarterly release of HCPCS Level II codes and short/long descriptors, the source for HCPCS code definitions and update history.
    3. 3.ICD-10-CM Full Code List. Centers for Medicare & Medicaid Services (CMS). Retrieved Aug 11, 2026.CMS's complete ICD-10-CM diagnosis code list, used to cross-reference diagnosis codes associated with this procedure or service.
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