ICD-10-CM Tabular Index · Chapter 1 · FY 2027 A80–A89
Viral and prion infections of the central nervous system (A80-A89) ICD-10-CM
The A80–A89 section covers viral and prion infections of the central nervous system with 60 ICD-10-CM diagnosis codes, of which 48 are billable in fiscal year 2027. The section is organized into the 10 code ranges listed below.
✓ Built from the official CMS FY 2027 datasetEffective Oct 1, 2026 – Sep 30, 2027
10
Code Ranges
60
Diagnosis Codes
48
Billable Codes
A80–A89
Code Range
Type 1 Excludes
A type 1 excludes note is a pure excludes note. It means "NOT CODED HERE!" An Excludes1 note indicates that the code excluded should never be used at the same time as the code above the Excludes1 note. An Excludes1 is used when two conditions cannot occur together, such as a congenital form versus an acquired form of the same condition.
The info icon previews the code ranges inside each row and its instructional notations from the official Tabular List.
About the A80–A89 Code Range
These viral and prion infections affect the central nervous system. The categories include polio, rabies, brain inflammation caused by a virus, and viral infections of the membranes around the central nervous system.
A80 separates acute polio by whether paralysis occurs. Its paralytic subdivisions distinguish vaccine association from wild virus origin. A81 groups named atypical infections, including Creutzfeldt-Jakob disease. A82 distinguishes sylvatic and urban rabies.
A83 and A84 separate mosquito-borne from tick-borne viral encephalitis, or brain inflammation caused by a virus. A85 groups other specified viral encephalitis, while A86 is unspecified viral encephalitis. A87 divides viral meningitis by named or unspecified type. A88 groups other specified viral infections of the central nervous system; A89 is an unspecified viral infection there.
Questions About This Page
How many codes are in the A80-A89 range?
The A80-A89 range contains 60 ICD-10-CM diagnosis codes in FY 2027. 48 of them are billable, and the rest are category headers that organize the section.
What conditions does A80-A89 cover?
The range covers viral and prion infections of the central nervous system. The code ranges listed above break it into groups of related conditions, and each one links to its own page with the full code list.
A type 1 excludes note is a pure excludes note. It means "NOT CODED HERE!" An Excludes1 note indicates that the code excluded should never be used at the same time as the code above the Excludes1 note. An Excludes1 is used when two conditions cannot occur together, such as a congenital form versus an acquired form of the same condition.
This note appears immediately under a three character code title to further define, or give examples of, the content of the category.
diseases of the central nervous system caused by prions
Use Additional Code
The “use additional code” indicates that a secondary code could be used to further specify the patient’s condition. This note is not mandatory and is only used if enough information is available to assign an additional code.
This note appears immediately under a three character code title to further define, or give examples of, the content of the category.
mosquito-borne viral meningoencephalitis
Type 2 Excludes
A type 2 excludes note represents "Not included here". An excludes2 note indicates that the condition excluded is not part of the condition represented by the code, but a patient may have both conditions at the same time. When an Excludes2 note appears under a code, it is acceptable to use both the code and the excluded code together, when appropriate.
This note appears immediately under a three character code title to further define, or give examples of, the content of the category.
specified viral encephalomyelitis NEC
specified viral meningoencephalitis NEC
Type 1 Excludes
A type 1 excludes note is a pure excludes note. It means "NOT CODED HERE!" An Excludes1 note indicates that the code excluded should never be used at the same time as the code above the Excludes1 note. An Excludes1 is used when two conditions cannot occur together, such as a congenital form versus an acquired form of the same condition.
These terms are the conditions for which that code is to be used. The terms may be synonyms of the code title, or, in the case of "other specified" codes, the terms are a list of the various conditions assigned to that code. The inclusion terms are not necessarily exhaustive. Additional terms found only in the Alphabetic Index may also be assigned to a code.
A type 1 excludes note is a pure excludes note. It means "NOT CODED HERE!" An Excludes1 note indicates that the code excluded should never be used at the same time as the code above the Excludes1 note. An Excludes1 is used when two conditions cannot occur together, such as a congenital form versus an acquired form of the same condition.
meningitis due to herpesvirus [herpes simplex] B00.3
meningitis due to herpesvirus [herpes simplex] B00.3
A type 1 excludes note is a pure excludes note. It means "NOT CODED HERE!" An Excludes1 note indicates that the code excluded should never be used at the same time as the code above the Excludes1 note. An Excludes1 is used when two conditions cannot occur together, such as a congenital form versus an acquired form of the same condition.
