WEST NILE FEVER
(West Nile virus infection, WNV)

Clinical Criteria
Any person with Fever
OR
At least one of the following two:
– Encephalitis
– Meningitis

Laboratory Criteria
- Laboratory test for case confirmation
At least one of the following four:
– Isolation of WNV from blood or CSF
– Detection of WNV nucleic acid in blood or CSF
– WNV specific antibody response (IgM) in CSF
– WNV IgM high titre AND detection of WNV IgG , AND confirmation by neutralisation
- Laboratory test for a probable case
WNV specific antibody response in serum
Laboratory results need to be interpreted according to flavivirus vaccination status

Epidemiological Criteria
At least one of the following two epidemiological links:
– Animal to human transmission (residing, having visited or having been exposed to
mosquito bites in an area where WNV is endemic in horses or birds)
– Human to human transmission (vertical transmission, blood transfusion, transplants)

Case Classification
A. Possible case   NA
B. Probable case
Any person meeting the clinical criteria AND with at least one of the following two:
– an epidemiological link
– a laboratory test for a probable case
C. Confirmed case
Any person meeting the laboratory criteria for case confirmation