ICD-10 Code A83.5 – California Encephalitis (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code A83.5 – California encephalitis
What it is
A83.5 identifies California encephalitis, a mosquito-borne viral encephalitis. Use it when the record documents this specific arboviral infection affecting the brain.
Clinical signs
Clinical features vary; refer to documentation. Typical encephalitis findings may include fever, headache, altered mental status, seizures, or neurologic deficits, but you should code only when the diagnosis is stated.
When to use this code
Use A83.5 when the clinician documents California encephalitis, including suspected or confirmed cases recorded as the final diagnosis. It may also apply when the note clearly identifies the infection as California encephalitis rather than a nonspecific viral encephalitis. Check documentation for the exact organism or syndrome wording.
Do not use for
Do not use this code for unspecified encephalitis, meningitis, or other arboviral infections unless California encephalitis is specifically documented. If the chart only says “viral encephalitis,” use the more general code instead.
Coding tip
Look for the exact disease name in the assessment or discharge summary before assigning A83.5.