National case definition: West Nile virus

Date of last revision/review: September 2008

National reporting

Probable and confirmed cases of disease should be notified.

Type of surveillance

Routine case-by-case notification to the federal level

Case classification

West Nile Virus Neurological Syndrome (WNNS)

Confirmed case

Clinical criteria AND at least one of the confirmed case diagnostic test criteria

Probable case

Clinical criteria AND at least one of the probable case diagnostic test criteria

Suspect case

Clinical criteria in the absence of or pending diagnostic test criteria AND in the absence of any other obvious cause

Clinical criteria

History of exposure in an area where West Nile virus (WNV) activity is occurring (see Comments section)

or

history of exposure to an alternative mode of transmission (see Comments section)

and

onset of fever

and

recent onset of at least one of the following:

West Nile Virus Non-Neurological Syndrome (WN Non-NS)

Confirmed case

Clinical criteria and at least one of the confirmed case diagnostic test criteria

Probable case

Clinical criteria and at least one of the probable case diagnostic test criteria

Suspect case

Clinical criteria in the absence of or pending diagnostic test criteria and in the absence of any other obvious cause

Clinical Criteria

History of exposure in an area where WN virus (WNV) activity is occurring

or

history of exposure to an alternative mode of transmission

and

at least two of the following:

West Nile Virus Asymptomatic Infection (WNAI)

Confirmed case

Confirmed case diagnostic test criteria in the absence of clinical criteria

Probable case

Probable case diagnostic test criteria in the absence of clinical criteria

Confirmed case diagnostic test criteria

It is currently recommended that health jurisdictions/authorities use the Confirmed Case Diagnostic Test Criteria to confirm index cases (locally acquired) in their area each year; for subsequent cases, health jurisdictions/authorities could use the Probable Case Diagnostic Test Criteria to classify cases in their area as “confirmed”, for the purposes of surveillance.  Throughout the remainder of the transmission season health jurisdictions/authorities may wish to document PRN antibody titres to West Nile virus in a proportion of cases, to be determined by that health jurisdiction/authority, in order to rule out the possibility of concurrent activity by other flaviviruses. (For further information on diagnostic testing algorithms for West Nile virus, see the section entitled Laboratory Specimen Diagnostic Testing Algorithm in Appendix 4 of the National Guidelines for Response to West Nile virus.)

At least one of the following:

or

or

or

or

Probable case diagnostic test criteria (see “Comments” section)

At least one of the following:

or

or

or

Laboratory comments

Sensitivity of NAT testing is approximately 50% when used on plasma/serum samples collected less than eight days after symptoms have been detected.  Individuals infected with WN virus display a low level of viremia (on average several thousand genome copies) for approximately one week after symptom onset.  The use of NAT testing on acute serum/plasma samples can complement IgM testing when used together to assay "early" acute specimens(1).

Clinical evidence

West Nile Neurological Syndrome (WNNS)

West Nile Virus Non-Neurological Syndrome (WN Non-NS)

West Nile Virus Asymptomatic Infection (WNAI)

ICD code(s)

ICD 10 code(s)

A92.3

ICD 9 code(s)

066.40, 066.41, 066.42, 066.49

Type of international reporting

Under Article 6 of the International Health Regulations (IHR) (2005), each State Party shall notify the World Health Organization (WHO) by way of the IHR National Focal Point,Footnote 1  and within 24 hours of assessment of public health information, of all events which may constitute a public health emergency of international concern within its territory in accordance with the decision instrument (Annex 2 of the IHRFootnote 2), as well as any health measure implemented in response to those events.

Note: If event does not meet the criteria for notification under Article 6 of the IHR, then other IHR-related reporting requirements may still apply with WHO and/or other States Parties, including those under Art. 7 (information-sharing during unexpected or unusual public health events), Art. 8 (consultation with WHO on public health events), Art. 9 (any public health risk that may cause international disease spread), Art. 10 (requests for verification from WHO), and Art. 44 (collaboration and assistance). 

Comments

References

Tilley P, Fox JD, Jayaraman GC, Preiksaitis JK. Nucleic acid test for West Nile virus RNA in plasma enhances rapid diagnosis of acute infection in symptomatic patients. J Infect Dis 2006;193:1361-1.

Sejvar J, Haddad MB, Tierney BC et al. Neurologic manifestations and outcome of West Nile virus infection. JAMA 2003;290:511-5.

Sejvar J. Bode AV, Marfin AA et al. West Nile virus-associated flaccid paralysis. Emerg Infect Dis 2003;9:788-93.

Burton JM, Kern RJ, Halliday W et al. Neurological manifestations of West Nile virus infection. Can J Neurol Sci 2004;31:185-93.

World Health Organization. International Health Regulations (2005). 3rd ed. Geneva, 2016

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