title: Evaluation of factors associated with positive IgM capture ELISA results in equids with clinical signs compatible with West Nile virus infection: 1,017 cases (2003).
abstract: OBJECTIVE
  To describe the prevalence of West Nile virus (WNV) infection and evaluate factors associated with positive IgM capture ELISA results in equids with clinical signs compatible with WNV infection.
  
  
  METHODS
  Retrospective case series.
  
  
  METHODS
  Laboratory submission forms from 1,104 equids tested for WNV in Colorado in 2003.
  
  
  METHODS
  Submission forms accompanying samples submitted for detection of WNV via IgM capture ELISA were obtained from the Colorado state veterinarian and diagnostic laboratories performing the tests. Data on signalment, clinical signs, history of vaccination against WNV, and assay results were collected from laboratory submission forms. Equids with clinical signs compatible with WNV infection in which IgM capture ELISA results were positive were considered as case equids.
  
  
  RESULTS
  1,104 equids were tested for WNV; 1,017 (92.1%) had clinical signs compatible with WNV infection. Among equids with clinical signs compatible with WNV infection, the odds of testing positive for WNV via IgM capture ELISA were lower in males and in vaccinated equids and higher in equids with moderate and severe illness, compared with females, unvaccinated equids, and equids with mild illness.
  
  
  CONCLUSIONS
  Among equids with clinical signs compatible with WNV infection, vaccination against WNV, severity of clinical signs, duration of illness, and region in Colorado were associated with increased risk of having a positive IgM capture ELISA result.
authors.affiliation: Animal Population Health Institute, College of Veterinary Medicine and Biomedical Sciences, Colorado State University, Fort Collins, CO 80523, USA.
authors.forename: Jennifer M
authors.initials: JM
authors.lastname: Tanner
authors.forename: Josie L
authors.initials: JL
authors.lastname: Traub-Dargatz
authors.forename: Ashley E
authors.initials: AE
authors.lastname: Hill
authors.forename: Hana
authors.initials: H
authors.lastname: Van Campen
authors.forename: Anthony P
authors.initials: AP
authors.lastname: Knight
authors.forename: Wayne E
authors.initials: WE
authors.lastname: Cunningham
authors.forename: M D
authors.initials: MD
authors.lastname: Salman
mesh_terms: D000818:Animals; D000914:Antibodies, Viral / Q000097:blood*; D003120:Colorado / Q000453:epidemiology; D016001:Confidence Intervals; D004797:Enzyme-Linked Immunosorbent Assay / Q000379:methods / Q000662:veterinary*; D005260:Female; D006734:Horse Diseases / Q000453:epidemiology*; D006736:Horses; D007075:Immunoglobulin M / Q000097:blood; D008297:Male; D016017:Odds Ratio; D012189:Retrospective Studies; D012307:Risk Factors; D016036:Seroepidemiologic Studies; D012720:Severity of Illness Index; D012737:Sex Factors; D014611:Vaccination / Q000662:veterinary; D014901:West Nile Fever / Q000453:epidemiology / Q000662:veterinary*; D014902:West Nile virus / Q000276:immunology*
chemical_list: D000914:Antibodies, Viral; D007075:Immunoglobulin M