2026 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 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

B05.0 is a billable ICD-10-CM diagnosis code for measles complicated by encephalitis. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026). 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

Tabular List NotesGuidance

Coding notes and annotation back-references applicable to this code.

Inclusion Terms

  • Postmeasles encephalitis

Index to Diseases and InjuriesGuidance

Alphabetical index entries that point to this code.

External Cause of Injuries IndexGuidance

References for this code in the External Cause of Injuries Index.

    • Encephalitis(chronic) (hemorrhagic) (idiopathic) (nonepidemic) (spurious) (subacute)
      • in (due to)
        • measles
    • Encephalitis(chronic) (hemorrhagic) (idiopathic) (nonepidemic) (spurious) (subacute)
      • postmeasles
    • Encephalomyelitis
      • postmeasles
    • Measles(black) (hemorrhagic) (suppressed)
      • with
        • encephalitis

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.

  • Measles Vaccine

    a live attenuated virus vaccine of chick embryo origin, used for routine immunization of children and for immunization of adolescents and adults who have not had measles or been immunized with live measles vaccine and have no serum antibodies against measles. children are usually immunized with measles-mumps-rubella combination vaccine. (from dorland, 28th ed)

  • Measles virus

    the type species of morbillivirus and the cause of the highly infectious human disease measles, which affects mostly children.

  • Measles-Mumps-Rubella Vaccine

    a combined vaccine used to prevent measles; mumps; and rubella.

  • Rubella

    an acute infectious disease caused by the rubella virus. the virus enters the respiratory tract via airborne droplet and spreads to the lymphatic system.

  • Rubella virus

    the type (and only) species of rubivirus causing acute infection in humans, primarily children and young adults. humans are the only natural host. a live, attenuated vaccine is available for prophylaxis.

  • Subacute Sclerosing Panencephalitis

    a rare, slowly progressive encephalitis caused by chronic infection with the measles virus. the condition occurs primarily in children and young adults, approximately 2-8 years after the initial infection. a gradual decline in intellectual abilities and behavioral alterations are followed by progressive myoclonus; muscle spasticity; seizures; dementia; autonomic dysfunction; and ataxia. death usually occurs 1-3 years after disease onset. pathologic features include perivascular cuffing, eosinophilic cytoplasmic inclusions, neurophagia, and fibrous gliosis. it is caused by the sspe virus, which is a defective variant of measles virus. (from adams et al., principles of neurology, 6th ed, pp767-8)

  • Viral Fusion Proteins

    proteins, usually glycoproteins, found in the viral envelopes of a variety of viruses. they promote cell membrane fusion and thereby may function in the uptake of the virus by cells.

  • Rubivirus

    a genus of the family togaviridae containing only one recognized species, rubella virus. transmission is primarily by aerosolization.

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 2017–2025No changes
FY 2026CurrentCurrent code set, no changesEffective October 1, 2025 through September 30, 2026.

Questions About B05.0Overview

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, 2025 through September 30, 2026.

What is the ICD-9 equivalent of B05.0?

Under the General Equivalence Mappings, measles complicated by encephalitis converts to ICD-9-CM 055.0 (postmeasles encephalitis). The mapping is a direct match.

Footnotes

[1] Not chronic - A diagnosis code that does not fit the criteria for chronic condition (duration, ongoing medical treatment, and limitations) is considered not chronic. Some codes designated as not chronic are acute conditions. Other diagnosis codes that indicate a possible chronic condition, but for which the duration of the illness is not specified in the code description (i.e., we do not know the condition has lasted 12 months or longer) also are considered not chronic.