Table 3.

Surveillance Case Definitions of WNV Infection^*

Confirmed case Febrile illness associated with neurologic manifestations plus at least 1 of the following Isolation of WNV from or demonstration of viral antigen or genetic material in tissue or body fluids IgM antibody to WNV in CSF† A ≥4-fold increase in antibody titer to WNV in paired CSF or serum samples Presence of both WNV-specific IgM and IgG antibodies in a single serum specimen Probable case A compatible illness that does not meet any of the laboratory criteria plus at least 1 of the following Serum IgM antibody against WNV Elevated IgG antibody against WNV in convalescent serum‡ Noncase An illness that does not meet the laboratory criteria plus a negative test result for IgM antibody against WNV in serum or CSF collected 8–21 days after onset of illness and/or negative WNV IgG antibody in serum collected ≥22 days after onset of illness

^*CSF = cerebrospinal fluid; ELISA = enzyme-linked immunosorbent assay; WNV = West Nile virus.

^†Detected by IgM capture ELISA.

^‡The ELISA for IgG is sensitive but nonspecific and should be confirmed with plaque reduction neutralization testing.