APPENDIX 1.

Case definitions for WNV meningitis/encephalitis
Suspect case: A person with a febrile illness AND associated neurological manifestations consistent with a diagnosis of viral meningitis or encephalitis that would include an altered mental status. Altered mental status could range from confusion to coma with or without additional signs of brain dysfunction (eg, paresis or paralysis, cranial nerve palsies, sensory deficits, abnormal reflexes, generalized convulsions and abnormal movements). A significant feature of WN viral encephalitis may be marked muscle weakness, therefore, WNV should be considered in the differential diagnosis of all suspected cases of acute flaccid paralysis or poliomyelitis. Patient history could include travel to an area with confirmed WNV activity in birds, horses, sentinel chickens, mosquitoes or humans.
Probable case: A person exhibiting clinical symptoms and travel history described in the suspect case definition and at least one of the following:
1. A fourfold or greater change in flavivirus HI or IgG ELISA titres in paired acute and convalescent sera.
2. A single serum sample with a P/N ratio of 3 or greater in a WNV IgM ELISA (and the P/N value obtained with WNV antigen is at least twice that demonstrated with other flavivirus antigens).
Note: If a titre 1:320 or greater is observed in a WNV HI test or an elevated titre is documented in a WNV IgG ELISA, the case may be considered probable with a confirmatory PRNT. However, if WNV cases have been previously documented in an area where the suspect case resides, then it may not be necessary to perform a confirmatory PRNT on single serum sample (or samples with high static titres) for the case to be designated as probable (see "Specimen collection and diagnostic algorithms").
Confirmed case: A confirmed case is a person with febrile illness and neurological symptoms consistent with the suspect case definition and at least one of the following:
1. A fourfold or greater change in HI or IgG ELISA titres, confirmed by the documentation of PRNT antibody titres to WNV in paired acute and convalescent sera or in convalescent sera only.
2. Isolation of WNV from or demonstration of WNV antigen or genomic sequences in tissue, blood, CSF or other body fluids.
3. Demonstration of IgM antibody to WNV in CSF by IgM-capture ELISA with confirmation by PRNT.

CSF Cerebrospinal fluid; HI Hemagglutination inhibition; Ig Immunoglobulin; PRNT Plaque-reduction neutralization test; WNV West Nile virus