866 — Viral Illness without MCC

MS-DRG 866, Viral Illness without MCC, is a medical DRG in MDC 18 (Infectious and Parasitic Diseases, Systemic or Unspecified Sites) under MS-DRG version 44.0, which applies to inpatient discharges from October 1, 2026 through September 30, 2027.

Its FY2027 relative weight is 0.8692, so Medicare's base payment for this DRG is about 0.87 times the average inpatient case (below average), before hospital-specific adjustments. The geometric mean length of stay is 2.7 days and the arithmetic mean is 3.5 days.

It belongs to a 2-level severity family: DRG 865 (with MCC, weight 1.3485) and DRG 866 (without MCC, weight 0.8692). The highest-severity level carries 1.6 times the weight of the lowest, which is why documenting CC and MCC conditions matters.

141 ICD-10-CM diagnosis codes are part of this DRG's grouping logic; they are listed below.