A83.1
BillableWestern equine encephalitis
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is A83.1 an HCC code?
No. A83.1 is a billable ICD-10-CM code but does not map to any HCC category in V28, V24, ESRD, or RxHCC.
This code does not map to an HCC category in any model (V28, V24, ESRD, RxHCC).
What This Code Means
A83.1 is the ICD-10-CM diagnosis code for western equine encephalitis. Western equine encephalitis is a viral infection that causes inflammation of the brain, transmitted to humans through mosquito bites, primarily occurring in western North America. Symptoms include fever, headache, and neurological complications ranging from mild to severe. A83.1 sits in the ICD-10-CM chapter for certain infectious and parasitic diseases (a00-b99), within the section covering viral and prion infections of the central nervous system (a80-a89).
A83.1 is a billable ICD-10-CM code but does not map to a payment HCC under the CMS-HCC V28, V24, ESRD, or RxHCC risk adjustment models. It can be reported on Medicare Advantage encounter data submissions but it does not contribute to a beneficiary's RAF score and therefore does not affect risk-adjusted payments to the plan.
Verify the specific type of equine encephalitis documented (Western, Eastern, or Venezuelan) as each has a distinct ICD-10-CM code; do not assume based on geographic location alone.
HCC Buddy maintains structured V28 and V24 mapping, RAF weights, and MEAT documentation criteria for A83.1 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •Verify the specific type of equine encephalitis documented (Western, Eastern, or Venezuelan) as each has a distinct ICD-10-CM code; do not assume based on geographic location alone
- •Document whether this is the acute phase or if there are residual neurological complications, as sequelae may require additional coding with code category B94.8