866 MS-DRG: VIRAL ILLNESS WITHOUT MCC
MS-DRG 866 groups Medicare inpatient hospital stays for: VIRAL ILLNESS WITHOUT MCC. This is a medical MS-DRG. It falls under MDC 18 (Infectious and Parasitic Diseases, Systemic or Unspecified Sites).
Payment & Classification Data
Official CMS values from the FY2027 IPPS Final Rule Table 5.
| Major Diagnostic Category | MDC 18 — Infectious and Parasitic Diseases, Systemic or Unspecified Sites |
| DRG Type | Medical |
| Severity Level | None |
| Relative Weight | 0.8692 |
| Relative Weight (10% Cap Applied) | 0.8692 |
| Geometric Mean Length of Stay | 2.7 days |
| Arithmetic Mean Length of Stay | 3.5 days |
| Post-Acute Transfer DRG | No |
| Special Pay Transfer DRG | No |
Defining Codes (FY2027)
141 diagnosis codes can drive assignment here: A70, A74.81, A74.89, A74.9, A80.4, A90, A91, A92.0, A92.1, A92.30, A92.31, A92.32 and 129 more.
From the CMS MS-DRG Definitions Manual (Appendices B and E). Assignment also depends on severity, discharge status and the rest of the claim.
Contextual Map
Every relationship of 866 in one view: hierarchy, official tabular instructions in both directions, clinical classification, risk adjustment, MS-DRG participation, index terms and change history — each edge carrying the CMS source it derives from.
Major Diagnostic Category
- MDC 18 — Infectious and Parasitic Diseases, Systemic or Unspecified Sites[MDC]— CMS MS-DRG Definitions Manual · FY2027
Defining diagnoses (141)
- A70 — Chlamydia psittaci infections[Grouper diagnosis]— CMS MS-DRG Definitions Manual (Appendix B) · FY2027
- A74.81 — Chlamydial peritonitis[Grouper diagnosis]— CMS MS-DRG Definitions Manual (Appendix B) · FY2027
- A74.89 — Other chlamydial diseases[Grouper diagnosis]— CMS MS-DRG Definitions Manual (Appendix B) · FY2027
- A74.9 — Chlamydial infection, unspecified[Grouper diagnosis]— CMS MS-DRG Definitions Manual (Appendix B) · FY2027
- A80.4 — Acute nonparalytic poliomyelitis[Grouper diagnosis]— CMS MS-DRG Definitions Manual (Appendix B) · FY2027
- A90 — Dengue fever [classical dengue][Grouper diagnosis]— CMS MS-DRG Definitions Manual (Appendix B) · FY2027
- A91 — Dengue hemorrhagic fever[Grouper diagnosis]— CMS MS-DRG Definitions Manual (Appendix B) · FY2027
- A92.0 — Chikungunya virus disease[Grouper diagnosis]— CMS MS-DRG Definitions Manual (Appendix B) · FY2027
- and 133 more
DRG family
- DRG 865 — VIRAL ILLNESS WITH MCC[DRG family]: “VIRAL ILLNESS WITH MCC — same CMS DRG family (865-866), split by severity.”— CMS MS-DRG Definitions Manual (DRG family 865-866) · FY2027
Read from: CMS MS-DRG Definitions Manual (incl. Appendix B diagnosis index, Appendix C CC/MCC list, Appendix E procedure index) and IPPS Final Rule tables — v44. All data sources · How to read the labels