ICD-10-CM 2027
ICD-10 code for slow virus infection
Atypical virus infection of central nervous system, unspecified
From the official ICD-10-CM alphabetic index entry “Infection, infected, infective (opportunistic) › slow virus”. Page updated September 29, 2026.
About coding slow virus infection
The ICD-10-CM code for slow virus infection is A81.9 (Atypical virus infection of central nervous system, unspecified). The official index lists 1 more specific code, so check the documentation for details such as type, cause, site or severity before settling on A81.9.
Within A81, choose A81.9 (Atypical virus infection of central nervous system, unspecified) only when documentation doesn't support a more specific option: Creutzfeldt-Jakob disease (A81.0), subacute sclerosing panencephalitis (A81.1), progressive multifocal leukoencephalopathy (A81.2) and other atypical virus infections of central nervous system (A81.8).
Use an additional code, if applicable, to identify: dementia with anxiety (F02.84, F02.A4, F02.B4, F02.C4), dementia with behavioral disturbance (F02.81-, F02.A1-, F02.B1-, F02.C1-), dementia with mood disturbance (F02.83, F02.A3, F02.B3, F02.C3), dementia with psychotic disturbance (F02.82, F02.A2, F02.B2, F02.C2), dementia without behavioral disturbance (F02.80, F02.A0, F02.B0, F02.C0) and 1 more.
As a secondary diagnosis it is a CC (complication or comorbidity), which can move an inpatient stay into the "with CC" MS-DRG of its family, unless the principal diagnosis excludes it.
More specific slow virus infection codes (official index)
- specified NEC A81.89 — Other atypical virus infections of central nervous system
Common questions about slow virus infection ICD-10 codes
What is the ICD-10 code for slow virus infection?
- A81.9 — Atypical virus infection of central nervous system, unspecified. More specific codes apply when the documentation supports them: A81.89.
Is A81.9 billable?
- Yes. A81.9 is a billable/specific ICD-10-CM code valid for FY2027 (October 1, 2026 – September 30, 2027).
Can A81.9 be used as a principal diagnosis?
- Yes. The Medicare Code Editor doesn't restrict A81.9 as a principal diagnosis.
Is A81.9 a CC or MCC?
- A81.9 is a CC (complication or comorbidity) under MS-DRG v44.0, unless excluded by the principal diagnosis.