A77.41 ICD-10-CM Code: Ehrlichiosis chaffeensis [E. chaffeensis]
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FY 2026 Apr update / Certain infectious and parasitic diseases (A00-B99) / Rickettsioses (A75-A79)
A77.41
Billable / SpecificICD-10-CMOfficial ICD-10-CMCodebook guidanceEhrlichiosis chaffeensis [E. chaffeensis]
Ehrlichiosis chaffeensis is a tick-borne bacterial infection caused by Ehrlichia chaffeensis that affects white blood cells and can cause fever, headache, and muscle aches. It is transmitted through the bite of infected lone star ticks and can range from mild to severe illness.
CMS-HCC V28
00
RAF 0
CMS-HCC V24
00
RAF 0
ACA/HHS
00
RAF 0
ESRD/PACE
00
RAF 0
RXHCC
00
RAF 0
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Inclusion Terms
OfficialICD-10-CM does not list inclusion terms for A77.41 in this effective period.
Excludes 2
OfficialICD-10-CM does not list Excludes 2 notes for A77.41 in this effective period.
Related Child Codes
Includes
OfficialICD-10-CM does not list Includes notes for A77.41 in this effective period.
Excludes 1
Official- anaplasmosis [A. phagocytophilum] (A79.82)
- rickettsiosis due to Ehrlichia sennetsu (A79.81)
Code First
OfficialICD-10-CM does not list Code First sequencing instructions for A77.41 in this effective period.
Use Additional
OfficialICD-10-CM does not list Use Additional Code instructions for A77.41 in this effective period.
Code Also
OfficialICD-10-CM does not list Code Also instructions for A77.41 in this effective period.
Buddy Documentation Tip
Last updated: FY2026 ICD-10-CM Apr update, Apr 1, 2026 through Sep 30, 2026. CMS-HCC V28 is 100% phased in for payment year 2026.
Is A77.41 an HCC code?
No. A77.41 is a billable ICD-10-CM code but does not map to any HCC category in V28, V24, ESRD, or RxHCC.
Coder workflow notes
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This code does not map to an HCC category in any model (V28, V24, ESRD, RxHCC).
What This Code Means
A77.41 is the ICD-10-CM diagnosis code for ehrlichiosis chaffeensis [e. chaffeensis]. Ehrlichiosis chaffeensis is a tick-borne bacterial infection caused by Ehrlichia chaffeensis that affects white blood cells and can cause fever, headache, and muscle aches. It is transmitted through the bite of infected lone star ticks and can range from mild to severe illness. A77.41 sits in the ICD-10-CM chapter for certain infectious and parasitic diseases (a00-b99), within the section covering rickettsioses (a75-a79).
A77.41 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.
This code is specific to E. chaffeensis infection; do not use it for other Ehrlichia species (such as E. ewingii or E. phagocytophila), which have separate codes.
HCC Buddy maintains structured V28 and V24 mapping, RAF weights, and MEAT documentation criteria for A77.41 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •This code is specific to E. chaffeensis infection; do not use it for other Ehrlichia species (such as E. ewingii or E. phagocytophila), which have separate codes
- •Document the clinical presentation and severity in the medical record, as this may support medical necessity and help differentiate from other tick-borne illnesses that may present similarly