A83.3
BillableSt Louis encephalitis
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is A83.3 an HCC code?
No. A83.3 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
A83.3 is the ICD-10-CM diagnosis code for st louis encephalitis. St. Louis encephalitis is a viral infection transmitted by mosquitoes that causes inflammation of the brain, leading to symptoms such as fever, headache, confusion, and potentially serious neurological complications. This disease is most common in North America during summer and fall months. A83.3 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).
A83.3 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 diagnosis is specifically St. Louis encephalitis (not other forms of encephalitis) before assigning this code, as documentation must clearly distinguish it from other arboviral encephalitis conditions.
HCC Buddy maintains structured V28 and V24 mapping, RAF weights, and MEAT documentation criteria for A83.3 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •Verify the diagnosis is specifically St. Louis encephalitis (not other forms of encephalitis) before assigning this code, as documentation must clearly distinguish it from other arboviral encephalitis conditions
- •This code should be used in conjunction with any documented complications such as seizures, altered mental status, or other neurological manifestations that may require additional coding