DRG 866
Medical DRGViral Illness without MCC
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.
FY 2026 Payment Data
Official values from Table 5 of the FY 2026 IPPS Final Rule (CMS).
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.
| DRG | Title | Rel. Weight | GMLOS |
|---|---|---|---|
| 865 | Viral Illness with MCC | 1.4983 | 4 days |
| 866 | Viral Illness without MCCThis page | 0.8696 | 2.7 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
