Use of the VectorTest for Advanced Warning of Human West Nile Virus Cases in Mississippi

West Nile virus (WNV) continues to persist in Mississippi; 2012 was the worse year for human infections, with a total of 247 reported human cases and five deaths. Public health officials are keenly interested in ways to detect WNV in advance in their jurisdictions, so they can implement appropriate and timely mosquito control in affected areas. A total of 40,312 female Culex quinquefasciatus mosquitoes were collected by gravid traps in Mississippi in 2013 and 2014 and tested by VectorTest, a rapid immunochromatographic assay (“dip-stick” test) that is a highly specific and effective rapid threat assessment tool. This study evaluated if and to what extent VectorTest could provide advanced warning of impending human WNV cases in a specific area. These data were examined with regard to date of onset of human WNV cases to determine the predictive value of VectorTest for WNV activity. Both years, positive mosquito pools appeared before the vast majority (87.2%) of reported human cases. Overall, in 27 out of 37 human WNV cases (73.0%) occurring in our study sites, there was an average advanced warning of 26 days (range 11–53 days) as indicated by positive mosquito collections near the patient’s home. This operational health department study, although somewhat limited, reveals that mosquito sampling and testing can inform public health and mosquito control personnel of WNV activity in an area and of impending human cases.