2027 ICD-10-CM Diagnosis Code A83.2Eastern equine encephalitis
ICD-10-CM Codes›A00–B99›A80-A89›A83
- Billable — Valid for Submission
- MCC — Major Complication or Comorbidity
- Not Chronic
A83.2 is a billable ICD-10-CM diagnosis code for Eastern equine encephalitis. It is valid on HIPAA claims for fiscal year 2027 (October 1, 2026 through September 30, 2027) and groups to MS-DRG 23 through 24, 97 through 99. 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 174 closely related codes. Coders also document this condition as Eastern equine encephalitis virus infection. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Encephalitis and Viral infection.
Code Identity
Code Classification
Approximate SynonymsGuidance
Alternate terms and clinical phrases that map to this code.
- Eastern equine encephalitis virus infection
- Eastern equine encephalitis virus neuroinvasive disease
- Eastern equine encephalitis virus non-neuroinvasive disease
- Encephalitis caused by Alphavirus
- Invasive viral infectious disease
Instructional NotesGuidance
Instructions from the official ICD-10-CM Tabular List that apply to A83.2: its own notes plus those printed at A83, block A80-A89, and Chapter 1. A note printed at a category, block or chapter applies to every code under it.
Includes
Further defines, or gives examples of, the content of the category.
- mosquito-borne viral meningoencephalitis
- diseases generally recognized as communicable or transmissible
Excludes1
Not coded here: the excluded code is never reported together with this one, unless the two conditions are unrelated.
Excludes2
Not included here: the excluded condition is not part of this code, but a patient may have both, so both codes may be reported.
- carrier or suspected carrier of infectious disease (Z22.-)
- certain localized infections - see body system-related chapters
- infectious and parasitic diseases complicating pregnancy, childbirth and the puerperium (O98.-)
- infectious and parasitic diseases specific to the perinatal period (P35-P39)
- influenza and other acute respiratory infections (J00-J22)
Use Additional Code
Add a second code, after this one, to fully describe the condition.
- code to identify resistance to antimicrobial drugs (Z16.-)
Source: CMS ICD-10-CM Tabular List. How to read instructional notes.
Index to Diseases and InjuriesGuidance
Alphabetical index entries that point to this code.
Encephalitis (chronic) (hemorrhagic) (idiopathic) (nonepidemic) (spurious) (subacute) G04.90
Eastern equine A83.2
Encephalomyelitis See Also: Encephalitis; G04.90
Clinical ClassificationClinical
AHRQ’s CCSR groups this code into broader clinical categories.
Clinical InformationClinical
Encephalomyelitis, Eastern Equine
a form of arboviral encephalitis (primarily affecting equines) endemic to eastern regions of north america. the causative organism (encephalomyelitis virus, eastern equine) may be transmitted to humans via the bite of aedes mosquitoes. clinical manifestations include the acute onset of fever, headache, altered mentation, and seizures followed by coma. the condition is fatal in up to 50% of cases. recovery may be marked by residual neurologic deficits and epilepsy. (from joynt, clinical neurology, 1996, ch26, pp9-10)
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 A83.2 to ICD-9-CMHistory
The closest ICD-9-CM equivalents under the General Equivalence Mappings.
Code HistoryHistory
Questions About A83.2Overview
What is the ICD-10 code for Eastern equine encephalitis?
The ICD-10-CM code for Eastern equine encephalitis is A83.2 (sometimes written as A832). It is billable on HIPAA-covered claims from October 1, 2026 through September 30, 2027.
Is A83.2 (Mosquito-borne viral encephalitis) a billable code?
Yes. This is a billable ICD-10-CM code, specific enough to report Eastern equine encephalitis on HIPAA-covered claims from October 1, 2026 through September 30, 2027.
What MS-DRG does A83.2 group to?
When Eastern equine encephalitis is the principal diagnosis on an inpatient stay, it groups to MS-DRG 24, 98, 99, 23, 97, with relative weights from 1.5249 to 5.7422 depending on complications. Higher weights mean higher Medicare reimbursement.
Is A83.2 a CC or MCC?
CMS lists A83.2 as an MCC (major complication or comorbidity) for FY 2027. 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 174 closely related codes in its exclusion list.
Can A83.2 be reported with G14?
Not as a rule. The Excludes1 note at block A80-A89, which applies to A83.2, lists "postpolio syndrome (G14)". An Excludes1 note means the excluded code is never reported together with this one; the only exception is when the two conditions are unrelated to each other (Official Guidelines, Section I.A.12.a).
