California encephalitis

This code represents California encephalitis, a viral infection of the brain caused by the California serogroup of bunyaviruses, primarily transmitted by mosquitoes. It typically presents with fever, headache, nausea, vomiting, and neurological symptoms such as seizures, disorientation, or paralysis, particularly in children.

Assign this code when documentation confirms a diagnosis of California encephalitis. This diagnosis is often supported by laboratory findings, such as serology or PCR, identifying California serogroup viruses, alongside characteristic clinical signs and symptoms.

• Ensure the documentation specifies "California encephalitis" to differentiate from other forms of viral encephalitis.
• Do not confuse with other arboviral encephalitides (e.g., West Nile, St. Louis) which have distinct ICD-10-CM codes.
• Code any associated neurological complications, such as seizures (G40.-), as secondary diagnoses.