Table 1: Diagnostic Criteria for Encephalitis and Encephalopathy of Presumed Infectious or Autoimmune Aetiology (extracted from Venkatesan et al. [2])

Major Criterion (required):
Patients presenting to medical attention with altered mental status (defined as decreased or altered level of consciousness, lethargy or personality change) lasting ≥24 h with no alternative cause identified.
Minor Criteria (2 required for possible encephalitis; ≥3 required for probable or confirmeda encephalitis):
- Documented fever ≥38C (100.4F) within the 72 h before or after presentation
- Generalized or partial seizures not fully attributable to a pre-existing seizure disorder
- New onset of focal neurologic findings
- CSF WBC count ≥5/cubic mm
- Abnormality of brain parenchyma on neuroimaging suggestive of encephalitis that is either new from prior studies or appears acute in onset
- Abnormality on electroencephalography that is consistent with encephalitis and not attributable to another cause.

Abbreviations: CNS: Central Nervous System, CSF: Cerebral Spinal Fluid, EEG: Electroencephalogram, RBC: Red Blood Cell, WBC: White Blood Cell

a Confirmed encephalitis requires one of the following: (1) Pathologic confirmation of brain inflammation consistent with encephalitis; (2) Defined pathologic, microbiologic, or serologic evidence of acute infection with a microorganism strongly associated with encephalitis from an appropriate clinical specimen; or (3) Laboratory evidence of an autoimmune condition strongly associated with encephalitis.