St. Louis encephalitis

This code represents an acute arboviral infection of the central nervous system caused by the St. Louis encephalitis virus. It typically manifests as a febrile illness, headache, and can progress to meningitis, encephalitis, or meningoencephalitis. The disease is transmitted to humans through the bite of infected mosquitoes, primarily Culex species.

Use this code for confirmed cases of St. Louis encephalitis, where diagnostic testing (e.g., serology, PCR) has identified the St. Louis encephalitis virus as the causative agent. This code is appropriate when the patient presents with neurological symptoms such as altered mental status, seizures, or focal neurological deficits in the context of a positive St. Louis encephalitis diagnosis. Documentation should clearly state the diagnosis of St. Louis encephalitis.

• Do not use this code for suspected cases without definitive laboratory confirmation.
• Distinguish from other arboviral encephalitides (e.g., West Nile encephalitis) which have separate codes.
• Sequence this code as the primary diagnosis when St. Louis encephalitis is the reason for the encounter.