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ALGORITHM FOR LOCAL HEALTH DEPARTMENT REPORTING OF WEST NILE VIRUS
NEW WEST NILE VIRUS LABORATORY RESULT RECEIVED3
WEST NILE VIRUS ANTIBODY RESULT
NAAT POSITIVE BLOOD DONOR
SERUM
CSF
WNV IgG Positive only
Yes
NOT A CASE of West Nile Virus Disease If the patient is WNV IgM negative and has symptoms consider alternative diagnosis such as: Viral Encephalitis and/or Meningitis or Bacterial Encephalitis and/or Meningitis
No
WNV IgM Positive and
the patient has clinical symptoms consistent with West Nile Virus Disease?1
Yes
No
Single Serum
PROBABLE
West Nile Virus Disease
WNV IgM Positive and
the patient has clinical symptoms consistent with West Nile Virus Disease?1
No
Yes
CSF Collected?
No
Did the patient have clinical symptoms consistent with West Nile Virus Disease on or around the time of blood donation?1
Paired Sera
If not already tested , submit to MDCH Bureau of Labs for Arboviral Testing (517) 335‐8067
Alternative: If commercial lab testing used, see interpretation appendix2
WNV IgM
Positive
Yes
No
Stable titer
Four‐
fold rise in titer
CONFIRMED
West Nile Virus Disease
PROBABLE
West Nile Virus Disease2
No
CONFIRMED
West Nile Virus Disease
NOT A CASE of
West Nile Virus Disease
Uninterpretable Yes
Negative result for other IgM
antibodies in CSF for arboviruses
endemic to the region where exposure occurred?
No/not done
Yes
Yes
Plaque Reduction
Neutralization Test
(PRNT) Antibody Detected?
Yes
CONFIRMED
West Nile Virus Disease
No
NOT A CASE of
West Nile Virus Disease
September 2012
APPENDIX
1. A clinically compatible case of arboviral disease is defined as follows: • Neuroinvasive disease • Fever (≥100.4°F or 38°C) as reported by the patient or a health‐care provider, AND
• Meningitis, encephalitis, acute flaccid paralysis, or other acute signs of central or peripheral neurologic dysfunction, as documented by a physician, AND
• Absence of a more likely clinical explanation.
• Non‐neuroinvasive disease • Fever (≥100.4°F or 38°C) as reported by the patient or a health‐care provider, AND
• Absence of neuroinvasive disease, AND
• Absence of a more likely clinical explanation.
2. Most commercially available tests methods use CDC developed reagents and protocols.
• Commercial testing may not be specific for WNV amongst other flaviviruses.
• Presence of IgM antibodies in a single serum sample will not confirm a recent infection, because IgM antibodies can persist in serum for up to 500 days post‐onset. Patient with a clinically compatible illness may be classified as a probable case of WNV, assuming WNV activity is present at the time of the illness onset.
• Presence of IgM antibodies in a single serum sample in a patient with a negative IgM antibody result in CSF will not confirm a recent infection, but patients with a clinically compatible illness may be classified as a probable case of WNV, assuming WNV activity is present in the population at the time of the illness onset.
• IgM positive CSF specimens from commercial laboratories should be forwarded to MDCH lab for confirmation. 3. Laboratory Criteria for Diagnosis
• Isolation of virus from, or demonstration of specific viral antigen or nucleic acid in, tissue, blood, CSF, or other body fluid, OR
• Four‐fold or greater change in virus‐specific quantitative antibody titers in paired sera, OR
• Virus‐specific IgM antibodies in serum with confirmatory virus‐specific neutralizing antibodies in the same or a later specimen, OR
• Virus‐specific IgM antibodies in CSF and a negative result for other IgM antibodies in CSF for arboviruses endemic to the region where exposure occurred, OR • Virus‐specific IgM antibodies in CSF or serum
September 2012