A79.81
BillableRickettsiosis due to Ehrlichia sennetsu
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is A79.81 an HCC code?
No. A79.81 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
A79.81 is the ICD-10-CM diagnosis code for rickettsiosis due to ehrlichia sennetsu. This is a bacterial infection caused by Ehrlichia sennetsu, a type of organism transmitted through tick bites that causes fever and flu-like symptoms. It is a form of rickettsiosis, which is a group of diseases caused by small parasitic bacteria. A79.81 sits in the ICD-10-CM chapter for certain infectious and parasitic diseases (a00-b99), within the section covering rickettsioses (a75-a79).
A79.81 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 documentation specifies Ehrlichia sennetsu as the causative organism, as other Ehrlichia species have different codes (A79.0 for Ehrlichia chaffeensis, A79.1 for Ehrlichia ewingii).
HCC Buddy maintains structured V28 and V24 mapping, RAF weights, and MEAT documentation criteria for A79.81 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •Verify documentation specifies Ehrlichia sennetsu as the causative organism, as other Ehrlichia species have different codes (A79.0 for Ehrlichia chaffeensis, A79.1 for Ehrlichia ewingii)
- •Look for evidence of tick exposure or bite in the patient history, and consider coding the external cause if documented; this code should not be used if a different Ehrlichia species is identified