2027 ICD-10-CM Diagnosis Code B05.0Measles complicated by encephalitis

ICD-10-CM Codes›A00–B99›B00-B09›B05

ICD-10-CM B05.0
CMSSource: CMS FY 2027 ICD-10-CM dataset · Effective Oct 1, 2026 – Sep 30, 2027

B05.0 is a billable ICD-10-CM diagnosis code for measles complicated by encephalitis. It is valid on HIPAA claims for fiscal year 2027 (October 1, 2026 through September 30, 2027) and groups to MS-DRG 23 through 24, 97 through 99, 791, 793. As a secondary diagnosis, it counts as a major complication or comorbidity (MCC) and places an inpatient stay in the highest severity level of its MS-DRG family. It does not count, however, when the principal diagnosis is one of 22 closely related codes. Coders also document this condition as measles inclusion body encephalitis. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Encephalitis and Viral infection.

Code Identity

ICD-10-CM Code
B05.0
Billable Status
Yes — Valid for Submission
Code Describes
Measles complicated by encephalitis
Short Description
Measles complicated by encephalitis
Same as the full description in the CMS dataset.
Parent Code
B05
Measles

Code Classification

ChapterA00–B99Certain infectious and parasitic diseases
SectionB00-B09Viral infections characterized by skin and mucous membrane lesions
CategoryB05Measles
This CodeB05.0Measles complicated by encephalitis

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Measles inclusion body encephalitis
  • Post measles encephalitis
  • Post-infectious encephalitis
  • Sequela of infection caused by Morbillivirus

Instructional NotesGuidance

Instructions from the official ICD-10-CM Tabular List that apply to B05.0: its own notes plus those printed at B05 and Chapter 1. A note printed at a category, block or chapter applies to every code under it.

Includes

Further defines, or gives examples of, the content of the category.

From B05 Measles applies to 8 codes
  • morbilli
From Chapter 1 (A00-B99) Certain infectious and parasitic diseases applies to 1,068 codes
  • diseases generally recognized as communicable or transmissible

Applicable To

Conditions this code is used for: synonyms of the title or, for "other specified" codes, the conditions assigned to it. The list is not exhaustive.

  • Postmeasles encephalitis

Excludes1

Not coded here: the excluded code is never reported together with this one, unless the two conditions are unrelated.

From B05 Measles applies to 8 codes
  • subacute sclerosing panencephalitis (A81.1)

Excludes2

Not included here: the excluded condition is not part of this code, but a patient may have both, so both codes may be reported.

From Chapter 1 (A00-B99) Certain infectious and parasitic diseases applies to 1,068 codes
  • carrier or suspected carrier of infectious disease (Z22.-)
  • certain localized infections - see body system-related chapters
  • infectious and parasitic diseases complicating pregnancy, childbirth and the puerperium (O98.-)
  • infectious and parasitic diseases specific to the perinatal period (P35-P39)
  • influenza and other acute respiratory infections (J00-J22)

Use Additional Code

Add a second code, after this one, to fully describe the condition.

From Chapter 1 (A00-B99) Certain infectious and parasitic diseases applies to 1,068 codes
  • code to identify resistance to antimicrobial drugs (Z16.-)

Source: CMS ICD-10-CM Tabular List. How to read instructional notes.

Referenced in Other NotesGuidance

Instructional notes printed at other codes that name B05.0, its category, or a range that includes it.

Excludes1 3

These codes carry an Excludes1 note naming B05.0: they are not reported together with it, unless the two conditions are unrelated.

  • A85 Other viral encephalitis, not elsewhere classified
    encephalitis due to measles virus (B05.0)
  • G04.01 Postinfectious acute disseminated encephalitis and encephalomyelitis (postinfectious ADEM)
    post measles encephalitis (B05.0)
  • G05 Encephalitis, myelitis and encephalomyelitis in diseases classified elsewhere
    encephalitis, myelitis and encephalomyelitis (in) measles (B05.0)

Index to Diseases and InjuriesGuidance

Alphabetical index entries that point to this code.

Clinical ClassificationClinical

AHRQ’s CCSR groups this code into broader clinical categories.

CCSR NVS002
Encephalitis
Default principal diagnosis: inpatient Yes · outpatient Yes
CCSR INF008
Viral infection
Default principal diagnosis: inpatient No · outpatient No

Clinical InformationClinical

  • Measles

    a highly contagious infectious disease caused by morbillivirus, common among children but also seen in the nonimmune of any age, in which the virus enters the respiratory tract via droplet nuclei and multiplies in the epithelial cells, spreading throughout the mononuclear phagocyte system.

Patient EducationClinical

Encephalitis

Encephalitis is inflammation (swelling) of the brain. It can happen when an infection or medical condition that affects the brain activates your immune system. The inflammation can cause a wide range of symptoms. In extreme cases, it can lead to brain damage, stroke, or even death.

The full article covers:

  • What is encephalitis?
  • What causes encephalitis?
  • Who is more likely to get encephalitis?
  • What are the symptoms of encephalitis?
  • How is encephalitis diagnosed?
  • What are the treatments for encephalitis?
  • Can encephalitis be prevented?

Read the full article at MedlinePlus

Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.

Convert B05.0 to ICD-9-CMHistory

The closest ICD-9-CM equivalents under the General Equivalence Mappings.

ICD-9-CM
055.0 Postmeasles encephalitis
Exact Match The mapping is direct, with no qualifiers.

Code HistoryHistory

FY 2016AddedAdded to the ICD-10-CM code setEffective October 1, 2015, the first year of ICD-10-CM.
FY 2017–2026No changes
FY 2027CurrentCurrent code set, no changesEffective October 1, 2026 through September 30, 2027.

Questions About B05.0Overview

What is the ICD-10 code for measles complicated by encephalitis?

The ICD-10-CM code for measles complicated by encephalitis is B05.0 (sometimes written as B050). It is billable on HIPAA-covered claims from October 1, 2026 through September 30, 2027.

Is B05.0 (Measles) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report measles complicated by encephalitis on HIPAA-covered claims from October 1, 2026 through September 30, 2027.

What MS-DRG does B05.0 group to?

When measles complicated by encephalitis is the principal diagnosis on an inpatient stay, it groups to MS-DRG 793, 791, 24, 98, 99, 23, 97, with relative weights from 1.5249 to 5.7422 depending on complications. Higher weights mean higher Medicare reimbursement.

Is B05.0 a CC or MCC?

CMS lists B05.0 as an MCC (major complication or comorbidity) for FY 2027. Reported as a secondary diagnosis, it places the inpatient stay in the highest-weighted DRG of its severity family. It does not count when the principal diagnosis is one of the 22 closely related codes in its exclusion list.

Can B05.0 be reported with A81.1?

Not as a rule. The Excludes1 note at B05, which applies to B05.0, lists "subacute sclerosing panencephalitis (A81.1)". An Excludes1 note means the excluded code is never reported together with this one; the only exception is when the two conditions are unrelated to each other (Official Guidelines, Section I.A.12.a).