Expanded Molecular Testing on Patients with Suspected West Nile Virus Disease

Vector Borne Zoonotic Dis. 2019 Sep;19(9):690-693. doi: 10.1089/vbz.2018.2412. Epub 2019 May 13.


Most diagnostic testing for West Nile virus (WNV) disease is accomplished using serologic testing, which is subject to cross-reactivity, may require cumbersome confirmatory testing, and may fail to detect infection in specimens collected early in the course of illness. The objective of this project was to determine whether a combination of molecular and serologic testing would increase detection of WNV disease cases in acute serum samples. A total of 380 serum specimens collected ≤7 days after onset of symptoms and submitted to four state public health laboratories for WNV diagnostic testing in 2014 and 2015 were tested. WNV immunoglobulin M (IgM) antibody and RT-PCR tests were performed on specimens collected ≤3 days after symptom onset. WNV IgM antibody testing was performed on specimens collected 4-7 days after onset and RT-PCR was performed on IgM-positive specimens. A patient was considered to have laboratory evidence of WNV infection if they had detectable WNV IgM antibodies or WNV RNA in the submitted serum specimen. Of specimens collected ≤3 days after symptom onset, 19/158 (12%) had laboratory evidence of WNV infection, including 16 positive for only WNV IgM antibodies, 1 positive for only WNV RNA, and 2 positive for both. Of specimens collected 4-7 days after onset, 21/222 (9%) were positive for WNV IgM antibodies; none had detectable WNV RNA. These findings suggest that routinely performing WNV RT-PCR on acute serum specimens submitted for WNV diagnostic testing is unlikely to identify a substantial number of additional cases beyond IgM antibody testing alone.

Keywords: PCR; West Nile; surveillance.

MeSH terms

  • Adolescent
  • Adult
  • Aged
  • Aged, 80 and over
  • Antibodies, Viral / blood
  • Child
  • Child, Preschool
  • Female
  • Humans
  • Immunoglobulin M / blood
  • Male
  • Middle Aged
  • Reverse Transcriptase Polymerase Chain Reaction
  • West Nile Fever / diagnosis*
  • Young Adult


  • Antibodies, Viral
  • Immunoglobulin M