Duration of West Nile Virus Immunoglobulin M Antibodies up to 81 Months Following West Nile Virus Disease Onset

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  • 1 Arboviral Diseases Branch, Division of Vector-Borne Diseases, Centers for Disease Control and Prevention, Fort Collins, Colorado;
  • | 2 Epidemic Intelligence Service Program, CDC, Atlanta, Georgia;
  • | 3 Quest Diagnostics Infectious Disease, Inc., San Juan Capistrano, California;
  • | 4 Division of High-Consequence Pathogens and Pathology, CDC, Atlanta, Georgia

West Nile virus (WNV) IgM antibodies typically indicate a recent infection. However, WNV IgM antibodies can remain detectable for months to years following illness onset. We found that 23% (11/47) of samples tested with a WNV ELISA and 43% (20/47) of samples tested with WNV microsphere immunoassay (MIA) at 16–19 months following WNV illness onset were positive for IgM antibodies. The proportion of samples testing positive for WNV IgM by ELISA decreased over time, but 5% (2/44) of individuals remained positive at 60–63 months after their acute illness and 4% (2/50) were WNV IgM equivocal at 72–81 months. Testing by MIA showed the same general trend of decreased proportion positive over time though the rates of positivity were higher at most time points compared with the ELISA, including 6% (3/50) of participant’s samples identified as IgM positive by MIA at 72–81 months post their acute illness. With the MIA, there also was a high proportion of samples with nonspecific results at each time point; average of 23% across all time points. Clinicians and public health officials should consider these findings along with clinical and epidemiologic data when interpreting WNV IgM antibody test results.

Author Notes

Address correspondence to J. Erin Staples, Arboviral Diseases Branch, Division of Vector-Borne Diseases, Centers for Disease Control and Prevention, 3156 Rampart Road, Fort Collins, CO 80521. E-mail: estaples@cdc.gov

Disclosure: H. Prince was a full-time employee of Focus Diagnostics, a commercial provider of West Nile virus diagnostic tests, at the time this testing was conducted.

Disclaimer: The findings and conclusions of this report are those of the authors and do not necessarily represent the views of the Centers for Disease Control and Prevention.

Authors’ addresses: J. Erin Staples, Amanda J. Panella, Alison J. Basile, Janeen Laven, and Marc Fischer, Arboviral Diseases Branch, Division of Vector-Borne Diseases, Centers for Disease Control and Prevention, Fort Collins, CO, E-mails: auv1@cdc.gov, ahf6@cdc.gov, ajj1@cdc.gov, blu8@cdc.gov, and mxf2@cdc.gov. Katherine B. Gibney, Arboviral Diseases Branch, Division of Vector-Borne Diseases, Centers for Disease Control and Prevention, Fort Collins, CO, and Epidemic Intelligence Service Program, CDC, Atlanta, GA, E-mail: katherine.gibney@unimelb.edu.au. Harry E. Prince, Quest Diagnostics Infectious Disease, Inc., San Juan Capistrano, CA, E-mail: harry.e.prince@questdiagnostics.com. James J. Sejvar, Division of High-Consequence Pathogens and Pathology, CDC, Atlanta, GA, E-mail: zea3@cdc.gov.

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