A77.0
BillableSpotted fever due to Rickettsia rickettsii
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is A77.0 an HCC code?
No. A77.0 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
A77.0 is the ICD-10-CM diagnosis code for spotted fever due to rickettsia rickettsii. This is a serious bacterial infection transmitted by tick bites that causes fever, headache, and a characteristic spotted rash on the skin. It's also known as Rocky Mountain spotted fever and requires prompt antibiotic treatment. A77.0 sits in the ICD-10-CM chapter for certain infectious and parasitic diseases (a00-b99), within the section covering rickettsioses (a75-a79).
A77.0 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 confirms Rickettsia rickettsii as the causative organism; do not use this code for other spotted fever types (use A77.1-A77.9 for other Rickettsia species).
HCC Buddy maintains structured V28 and V24 mapping, RAF weights, and MEAT documentation criteria for A77.0 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •Verify documentation confirms Rickettsia rickettsii as the causative organism; do not use this code for other spotted fever types (use A77.1-A77.9 for other Rickettsia species)
- •This code indicates the specific pathogen and should be paired with appropriate manifestation codes (such as rash codes) if documented; check for any complications or secondary conditions that may require additional coding