DRG 866

Medical DRG

Viral Illness without MCC

TypeMedicalMDC18Dx Codes141

What is MS-DRG 866?

MS-DRG 866 is a Medical Medicare Severity Diagnosis Related Group under Major Diagnostic Category 18 (MDC 18) without a significant Complication or Comorbidity. It maps to 141 ICD-10-CM diagnosis codes. For FY 2026 it carries a relative weight of 0.8696 with a geometric mean length of stay of 2.7 days and an arithmetic mean of 3.5 days. Hospitals use this grouping to determine reimbursement for inpatient stays under Medicare.

Classification
Medical DRG
Diagnosis-driven grouping
Linked Codes
141 diagnosis
Billable Dx
100%
141 of 141 shown

FY 2026 Payment Data

Official values from Table 5 of the FY 2026 IPPS Final Rule (CMS).

Relative Weight
0.8696
Payment multiplier vs. average case (1.0)
Geometric Mean LOS
2.7 days
Used for transfer payment calculations
Arithmetic Mean LOS
3.5 days
Average length of stay
Post-Acute Transfer
No
Not subject to the transfer policy

Related MS-DRGs in This Severity Group

The same clinical condition is split into separate DRGs by complication severity. MCC pays more than CC, which pays more than no CC/MCC.

DRGTitleRel. WeightGMLOS
865Viral Illness with MCC1.49834 days
866Viral Illness without MCCThis page0.86962.7 days

Linked ICD-10-CM Diagnosis Mappings

  • A70

    Chlamydia psittaci infections

    BillableChapter 1
  • A74.81

    Chlamydial peritonitis

    BillableChapter 1
  • A74.89

    Other chlamydial diseases

    BillableChapter 1
  • A74.9

    Chlamydial infection, unspecified

    BillableChapter 1
  • A80.4

    Acute nonparalytic poliomyelitis

    BillableChapter 1
  • A90

    Dengue fever [classical dengue]

    BillableChapter 1
  • A91

    Dengue hemorrhagic fever

    BillableChapter 1
  • A92.0

    Chikungunya virus disease

    BillableChapter 1
  • A92.1

    O'nyong-nyong fever

    BillableChapter 1
  • A92.30

    West Nile virus infection, unspecified

    BillableChapter 1
  • A92.31

    West Nile virus infection with encephalitis

    BillableChapter 1
  • A92.32

    West Nile virus infection with other neurologic manifestation

    BillableChapter 1
  • A92.39

    West Nile virus infection with other complications

    BillableChapter 1
  • A92.4

    Rift Valley fever

    BillableChapter 1
  • A92.5

    Zika virus disease

    BillableChapter 1
  • A92.8

    Other specified mosquito-borne viral fevers

    BillableChapter 1
  • A92.9

    Mosquito-borne viral fever, unspecified

    BillableChapter 1
  • A93.0

    Oropouche virus disease

    BillableChapter 1
  • A93.1

    Sandfly fever

    BillableChapter 1
  • A93.2

    Colorado tick fever

    BillableChapter 1
  • A93.8

    Other specified arthropod-borne viral fevers

    BillableChapter 1
  • A94

    Unspecified arthropod-borne viral fever

    BillableChapter 1
  • A95.0

    Sylvatic yellow fever

    BillableChapter 1
  • A95.1

    Urban yellow fever

    BillableChapter 1
  • A95.9

    Yellow fever, unspecified

    BillableChapter 1
  • A96.0

    Junin hemorrhagic fever

    BillableChapter 1
  • A96.1

    Machupo hemorrhagic fever

    BillableChapter 1
  • A96.2

    Lassa fever

    BillableChapter 1
  • A96.8

    Other arenaviral hemorrhagic fevers

    BillableChapter 1
  • A96.9

    Arenaviral hemorrhagic fever, unspecified

    BillableChapter 1
  • A98.0

    Crimean-Congo hemorrhagic fever

    BillableChapter 1
  • A98.1

    Omsk hemorrhagic fever

    BillableChapter 1
  • A98.2

    Kyasanur Forest disease

    BillableChapter 1
  • A98.3

    Marburg virus disease

    BillableChapter 1
  • A98.4

    Ebola virus disease

    BillableChapter 1
  • A98.8

    Other specified viral hemorrhagic fevers

    BillableChapter 1
  • A99

    Unspecified viral hemorrhagic fever

    BillableChapter 1
  • B00.89

    Other herpesviral infection

    BillableChapter 1
  • B01.0

    Varicella meningitis

    BillableChapter 1
  • B01.81

    Varicella keratitis

    BillableChapter 1
  • B01.89

    Other varicella complications

    BillableChapter 1
  • B01.9

    Varicella without complication

    BillableChapter 1
  • B02.7

    Disseminated zoster

    BillableChapter 1
  • B02.8

    Zoster with other complications

    BillableChapter 1
  • B03

    Smallpox

    BillableChapter 1
  • B04

    Monkeypox

    BillableChapter 1
  • B05.1

    Measles complicated by meningitis

    BillableChapter 1
  • B05.4

    Measles with intestinal complications

    BillableChapter 1
  • B05.89

    Other measles complications

    BillableChapter 1
  • B05.9

    Measles without complication

    BillableChapter 1
  • B06.81

    Rubella pneumonia

    BillableChapter 1
  • B06.89

    Other rubella complications

    BillableChapter 1
  • B06.9

    Rubella without complication

    BillableChapter 1
  • B08.010

    Cowpox

    BillableChapter 1
  • B08.011

    Vaccinia not from vaccine

    BillableChapter 1
  • B08.04

    Paravaccinia, unspecified

    BillableChapter 1
  • B08.09

    Other orthopoxvirus infections

    BillableChapter 1
  • B08.20

    Exanthema subitum [sixth disease], unspecified

    BillableChapter 1
  • B08.21

    Exanthema subitum [sixth disease] due to human herpesvirus 6

    BillableChapter 1
  • B08.22

    Exanthema subitum [sixth disease] due to human herpesvirus 7

    BillableChapter 1
  • B08.3

    Erythema infectiosum [fifth disease]

    BillableChapter 1
  • B08.4

    Enteroviral vesicular stomatitis with exanthem

    BillableChapter 1
  • B08.60

    Parapoxvirus infection, unspecified

    BillableChapter 1
  • B08.61

    Bovine stomatitis

    BillableChapter 1
  • B08.62

    Sealpox

    BillableChapter 1
  • B08.69

    Other parapoxvirus infections

    BillableChapter 1
  • B08.70

    Yatapoxvirus infection, unspecified

    BillableChapter 1
  • B08.71

    Tanapox virus disease

    BillableChapter 1
  • B08.72

    Yaba pox virus disease

    BillableChapter 1
  • B08.79

    Other yatapoxvirus infections

    BillableChapter 1
  • B08.8

    Other specified viral infections characterized by skin and mucous membrane lesions

    BillableChapter 1
  • B09

    Unspecified viral infection characterized by skin and mucous membrane lesions

    BillableChapter 1
  • B25.8

    Other cytomegaloviral diseases

    BillableChapter 1
  • B25.9

    Cytomegaloviral disease, unspecified

    BillableChapter 1
  • B26.82

    Mumps myocarditis

    BillableChapter 1
  • B26.83

    Mumps nephritis

    BillableChapter 1
  • B26.85

    Mumps arthritis

    BillableChapter 1
  • B26.89

    Other mumps complications

    BillableChapter 1
  • B26.9

    Mumps without complication

    BillableChapter 1
  • B27.00

    Gammaherpesviral mononucleosis without complication

    BillableChapter 1
  • B27.01

    Gammaherpesviral mononucleosis with polyneuropathy

    BillableChapter 1
  • B27.02

    Gammaherpesviral mononucleosis with meningitis

    BillableChapter 1
  • B27.09

    Gammaherpesviral mononucleosis with other complications

    BillableChapter 1
  • B27.10

    Cytomegaloviral mononucleosis without complications

    BillableChapter 1
  • B27.11

    Cytomegaloviral mononucleosis with polyneuropathy

    BillableChapter 1
  • B27.12

    Cytomegaloviral mononucleosis with meningitis

    BillableChapter 1
  • B27.19

    Cytomegaloviral mononucleosis with other complication

    BillableChapter 1
  • B27.80

    Other infectious mononucleosis without complication

    BillableChapter 1
  • B27.81

    Other infectious mononucleosis with polyneuropathy

    BillableChapter 1
  • B27.82

    Other infectious mononucleosis with meningitis

    BillableChapter 1
  • B27.89

    Other infectious mononucleosis with other complication

    BillableChapter 1
  • B27.90

    Infectious mononucleosis, unspecified without complication

    BillableChapter 1
  • B27.91

    Infectious mononucleosis, unspecified with polyneuropathy

    BillableChapter 1
  • B27.92

    Infectious mononucleosis, unspecified with meningitis

    BillableChapter 1
  • B27.99

    Infectious mononucleosis, unspecified with other complication

    BillableChapter 1
  • B33.1

    Ross River disease

    BillableChapter 1
  • B33.3

    Retrovirus infections, not elsewhere classified

    BillableChapter 1
  • B33.4

    Hantavirus (cardio)-pulmonary syndrome [HPS] [HCPS]

    BillableChapter 1
  • B33.8

    Other specified viral diseases

    BillableChapter 1
  • B34.0

    Adenovirus infection, unspecified

    BillableChapter 1
  • B34.1

    Enterovirus infection, unspecified

    BillableChapter 1
  • B34.2

    Coronavirus infection, unspecified

    BillableChapter 1
  • B34.3

    Parvovirus infection, unspecified

    BillableChapter 1
  • B34.4

    Papovavirus infection, unspecified

    BillableChapter 1
  • B34.8

    Other viral infections of unspecified site

    BillableChapter 1
  • B34.9

    Viral infection, unspecified

    BillableChapter 1
  • B97.0

    Adenovirus as the cause of diseases classified elsewhere

    BillableChapter 1
  • B97.10

    Unspecified enterovirus as the cause of diseases classified elsewhere

    BillableChapter 1
  • B97.11

    Coxsackievirus as the cause of diseases classified elsewhere

    BillableChapter 1
  • B97.12

    Echovirus as the cause of diseases classified elsewhere

    BillableChapter 1
  • B97.19

    Other enterovirus as the cause of diseases classified elsewhere

    BillableChapter 1
  • B97.21

    SARS-associated coronavirus as the cause of diseases classified elsewhere

    BillableChapter 1
  • B97.29

    Other coronavirus as the cause of diseases classified elsewhere

    BillableChapter 1
  • B97.30

    Unspecified retrovirus as the cause of diseases classified elsewhere

    BillableChapter 1
  • B97.31

    Lentivirus as the cause of diseases classified elsewhere

    BillableChapter 1
  • B97.32

    Oncovirus as the cause of diseases classified elsewhere

    BillableChapter 1
  • B97.33

    Human T-cell lymphotrophic virus, type I [HTLV-I] as the cause of diseases classified elsewhere

    BillableChapter 1
  • B97.34

    Human T-cell lymphotrophic virus, type II [HTLV-II] as the cause of diseases classified elsewhere

    BillableChapter 1
  • B97.35

    Human immunodeficiency virus, type 2 [HIV 2] as the cause of diseases classified elsewhere

    BillableChapter 1
  • B97.39

    Other retrovirus as the cause of diseases classified elsewhere

    BillableChapter 1
  • B97.4

    Respiratory syncytial virus as the cause of diseases classified elsewhere

    BillableChapter 1
  • B97.5

    Reovirus as the cause of diseases classified elsewhere

    BillableChapter 1
  • B97.6

    Parvovirus as the cause of diseases classified elsewhere

    BillableChapter 1
  • B97.7

    Papillomavirus as the cause of diseases classified elsewhere

    BillableChapter 1
  • B97.81

    Human metapneumovirus as the cause of diseases classified elsewhere

    BillableChapter 1
  • B97.89

    Other viral agents as the cause of diseases classified elsewhere

    BillableChapter 1
  • J09.X3

    Influenza due to identified novel influenza A virus with gastrointestinal manifestations

    BillableChapter 10
  • J09.X9

    Influenza due to identified novel influenza A virus with other manifestations

    BillableChapter 10
  • J10.2

    Influenza due to other identified influenza virus with gastrointestinal manifestations

    BillableChapter 10
  • J10.81

    Influenza due to other identified influenza virus with encephalopathy

    BillableChapter 10
  • J10.82

    Influenza due to other identified influenza virus with myocarditis

    BillableChapter 10
  • J10.83

    Influenza due to other identified influenza virus with otitis media

    BillableChapter 10
  • J10.89

    Influenza due to other identified influenza virus with other manifestations

    BillableChapter 10
  • J11.2

    Influenza due to unidentified influenza virus with gastrointestinal manifestations

    BillableChapter 10
  • J11.81

    Influenza due to unidentified influenza virus with encephalopathy

    BillableChapter 10
  • J11.82

    Influenza due to unidentified influenza virus with myocarditis

    BillableChapter 10
  • J11.83

    Influenza due to unidentified influenza virus with otitis media

    BillableChapter 10
  • J11.89

    Influenza due to unidentified influenza virus with other manifestations

    BillableChapter 10
  • L44.4

    Infantile papular acrodermatitis [Gianotti-Crosti]

    BillableChapter 12
  • T88.1XXA

    Other complications following immunization, not elsewhere classified, initial encounter

    BillableChapter 19
  • Z21

    Asymptomatic human immunodeficiency virus [HIV] infection status

    BillableChapter 21