Interpretation

Presence of specific IgM-class antibodies to West Nile virus (WNV)is consistent with the acute phase of WNV meningitis or encephalitis. In the very early stages of acute WNV infection, IgM may be detectable in cerebrospinal fluid (CSF) before it becomes detectable in serum.

The absence of IgM antibodies to WNV may indicate absence of disease. However, specimens collected too early in the acute phase may be negative for IgM-class antibodies to WNV. If WNV central nervous system infection is suspected, a second specimen should be collected in 1 to 2 weeks and tested.

The presence of IgG-class antibodies to WNV may indicate recent or past central nervous system (CNS) infection with WNV. Clinical correlation is necessary.

This assay is unable to distinguish between intrathecal antibody synthesis and serum antibodies introduced into the CSF at the time of lumbar puncture or from a breakdown in the blood-brain barrier. Positive results should be interpreted with other laboratory and clinical data prior to a diagnosis of CNS infection.