A01.04
BillableTyphoid arthritis
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is A01.04 an HCC code?
Yes. A01.04 maps to Bone/Joint/Muscle/Severe Soft Tissue Infections/Necrosis under the CMS-HCC V28 risk adjustment model (and Bone/Joint/Muscle Infections/Necrosis under V24).
HCC Category Mapping
RAF weights shown are the community, non-dual, aged base weights from the CMS risk adjustment model file. Actual per-patient RAF contribution depends on member segment, interactions, and the model year used by the payer. V28 is the CMS-HCC model phased in over payment years 2024–2026; V24 remains in use during the transition and for historical data.
MEAT Criteria for A01.04
For A01.04to count as a valid HCC diagnosis in a given encounter, the provider's documentation must show MEAT: Monitor, Evaluate, Assess, or Treat. A diagnosis from a prior year does not carry forward automatically — it has to be re-documented and supported each calendar year.
- MMonitor: signs, symptoms, disease progression, or lab trending documented in the note
- EEvaluate: test results, medication response, or physical findings reviewed by the provider
- AAssess: explicit mention in the assessment or plan with acknowledgment of status
- TTreat: medication, referral, procedure, therapy, or counseling tied to the diagnosis
Only one of M/E/A/T is required to support the code, but the documentation must be specific enough to show that the provider actually addressed A01.04 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
A01.04 is the ICD-10-CM diagnosis code for typhoid arthritis. Typhoid arthritis is joint inflammation that develops as a complication of typhoid fever, a serious bacterial infection caused by Salmonella typhi. This condition causes pain, swelling, and stiffness in the affected joints during or after typhoid infection. A01.04 sits in the ICD-10-CM chapter for certain infectious and parasitic diseases (a00-b99), within the section covering intestinal infectious diseases (a00-a09).
Under the CMS-HCC V28 risk adjustment model, A01.04 maps to Bone/Joint/Muscle/Severe Soft Tissue Infections/Necrosis (HCC 92) with a community, non-dual, aged base RAF weight of 0.479. Under the older CMS-HCC V24 model, A01.04 maps to Bone/Joint/Muscle Infections/Necrosis (HCC 39) with a community, non-dual, aged base RAF weight of 0.401. V28 is the CMS-HCC risk adjustment model that reached 100% phase-in for payment year 2026, replacing V24 which was used during the PY2024–PY2025 transition.
This code should only be used when arthritis is documented as a direct complication of typhoid fever; do not use if arthritis is unrelated to the typhoid infection. Because A01.04 maps to a payment HCC, the provider's documentation must satisfy MEAT criteria (Monitor, Evaluate, Assess, or Treat) for the encounter to count toward the patient's Medicare Advantage risk adjustment score. When documentation is ambiguous, coders should issue a provider query rather than assume the highest-specificity variant.
HCC Buddy maintains structured V28 and V24 mapping, RAF weights, and MEAT documentation criteria for A01.04 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •This code should only be used when arthritis is documented as a direct complication of typhoid fever; do not use if arthritis is unrelated to the typhoid infection
- •Verify that the patient has confirmed typhoid fever diagnosis and that the arthritis manifestation is explicitly documented by the provider before assigning this code
Clinical Significance
Typhoid arthritis is a rare but clinically significant infectious arthritis caused by Salmonella typhi dissemination to joint spaces. It indicates systemic infection severity and can lead to joint destruction if not promptly treated with appropriate antibiotics and possible joint drainage.
Documentation Requirements
- ✓Documented Salmonella typhi infection with joint involvement
- ✓Specific joint(s) affected with clinical findings (swelling, erythema, limited range of motion)
- ✓Synovial fluid analysis results if performed (culture, cell count, crystal analysis to rule out gout)
- ✓Imaging of affected joint(s) showing effusion or destructive changes
- ✓Documentation of causal relationship between typhoid and the arthritis
Commonly Confused Codes
- •A02.23 (Salmonella arthritis) — Use A02.23 for non-typhi Salmonella joint infections; A01.04 is specifically for S. typhi arthritis
- •M00.9 (Pyogenic arthritis, unspecified) — Use A01.04 when the infectious arthritis is specifically attributed to typhoid fever
- •A01.00 (Typhoid fever, unspecified) — Use A01.04 when arthritis is a documented complication, not the unspecified typhoid code