2027 ICD-10-CM Diagnosis Code B00.4Herpesviral encephalitis
ICD-10-CM Codes›A00–B99›B00-B09›B00
- Billable — Valid for Submission
- MCC — Major Complication or Comorbidity
- Chronic Condition
B00.4 is a billable ICD-10-CM diagnosis code for herpesviral 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, 974 through 976. 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 13 closely related codes. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Encephalitis and Viral infection.
Code Identity
Code Classification
Approximate SynonymsGuidance
Alternate terms and clinical phrases that map to this code.
- Acute encephalitis
- Acute necrotizing encephalitis
- Acute viral encephalitis
- Dementia associated with viral encephalitis
- Dementia due to herpes encephalitis
- Encephalitis caused by Herpesvirus
- Encephalitis caused by human herpes simplex virus
- Herpes simiae encephalitis
- Herpes simplex meningitis
- Herpes simplex type 1 encephalitis
- Herpes simplex type 1 infection
- Herpes simplex type 2 encephalitis
- Herpes simplex type 2 infection
- Herpetic acute necrotizing encephalitis
- Meningoencephalitis caused by human herpes simplex virus
- Meningoencephalitis caused by virus
- Simian B disease
- Simian B encephalomyelitis
Instructional NotesGuidance
Instructions from the official ICD-10-CM Tabular List that apply to B00.4: its own notes plus those printed at B00 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.
- 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.
- Herpesviral meningoencephalitis
- Simian B disease
Excludes1
Not coded here: the excluded code is never reported together with this one, unless the two conditions are unrelated.
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.
- 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.
- 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 B00.4, its category, or a range that includes it.
Excludes1 2
These codes carry an Excludes1 note naming B00.4: they are not reported together with it, unless the two conditions are unrelated.
Excludes2 7
These codes carry an Excludes2 note naming B00.4: its condition is not part of those codes, and both may be reported when the patient has both.
- B10.0 Other human herpesvirus encephalitisherpes encephalitis NOS (B00.4)
- B10.0 Other human herpesvirus encephalitisherpes simplex encephalitis (B00.4)
- B10.0 Other human herpesvirus encephalitishuman herpesvirus encephalitis (B00.4)
- B10.0 Other human herpesvirus encephalitissimian B herpes virus encephalitis (B00.4)
- B10 Other human herpesvirusesherpes simplex (B00.-) names B00.-, which includes this code
- B10 Other human herpesviruseshuman herpesvirus NOS (B00.-) names B00.-, which includes this code
- B10 Other human herpesviruseshuman herpesvirus 1 and 2 (B00.-) names B00.-, which includes this code
Index to Diseases and InjuriesGuidance
Alphabetical index entries that point to this code.
Disease, diseased See Also: Syndrome;
simian B B00.4
Meningoencephalitis See Also: Encephalitis; G04.90
herpes B00.4
Clinical ClassificationClinical
AHRQ’s CCSR groups this code into broader clinical categories.
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 B00.4 to ICD-9-CMHistory
The closest ICD-9-CM equivalents under the General Equivalence Mappings.
Code HistoryHistory
Questions About B00.4Overview
What is the ICD-10 code for herpesviral encephalitis?
The ICD-10-CM code for herpesviral encephalitis is B00.4 (sometimes written as B004). It is billable on HIPAA-covered claims from October 1, 2026 through September 30, 2027.
Is B00.4 (Herpesviral [herpes simplex] infections) a billable code?
Yes. This is a billable ICD-10-CM code, specific enough to report herpesviral encephalitis on HIPAA-covered claims from October 1, 2026 through September 30, 2027.
What MS-DRG does B00.4 group to?
When herpesviral encephalitis is the principal diagnosis on an inpatient stay, it groups to MS-DRG 793, 791, 24, 98, 974, 976, 99, 975, 23, 97, with relative weights from 0.7879 to 5.7422 depending on complications. Higher weights mean higher Medicare reimbursement.
Is B00.4 a CC or MCC?
CMS lists B00.4 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 13 closely related codes in its exclusion list.
Can B00.4 be reported with B10.01?
Not as a rule. The Excludes1 note on B00.4 lists "herpesviral encephalitis due to herpesvirus 6 and 7 (B10.01, B10.09)". 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).
