Abstract
West Nile virus (WNV) is the leading cause of domestically acquired arboviral disease. To develop real-time WNV forecasts of infected mosquitoes and human cases. Real-time forecasts of WNV in 4 geographically dispersed locations in the United States were generated using a WNV model-inference forecasting system previously validated with retrospective data. Analysis was performed to evaluate how observational reporting delays of mosquito WNV assay results and human medical records were associated with real-time forecast accuracy. Mosquitoes positive for WNV and human cases. Delays in reporting mosquito WNV assay results and human medical records and the association of these delays with real-time WNV forecast accuracy. Substantial delays in data reporting exist for both infected mosquitoes and human WNV cases. For human cases, confirmed data (n = 37) lagged behind the onset of illness by a mean (SD) of 5.5 (2.3) weeks (range, 2-14 weeks). These human case reporting lags reduced mean forecast accuracy for the total number of human cases over the season in 110 simulated outbreaks for 2 forecasting systems by 26% and 14%, from 2 weeks before to 3 weeks after the predicted peak of infected mosquitoes. This period is the time span during which 47% of human cases are reported. Of 7064 mosquito pools, 500 (7%) tested positive; the reporting lag for these data associated with viral testing at a state laboratory was a mean (SD) of 6.6 (2.6) days (range, 4-11 days). This reporting lag was associated with decreased mean forecast accuracy for the 3 mosquito infection indicators, timing, magnitude, and season, by approximately 5% for both forecasting systems. Delays in reporting human WNV disease and infected mosquito information are associated with difficulties in outbreak surveillance and decreased real-time forecast accuracy. Infected mosquito lags were short enough that skillful forecasts could still be generated for mosquito infection indicators, but the human WNV case lags were too great to support accurate forecasting in real time. Forecasting WNV is potentially an important evidence-based decision support tool for public health officials and mosquito abatement districts; however, to operationalize real-time forecasting, more resources are needed to reduce human case reporting lags between illness onset and case confirmation.
Highlights
IntroductionDuring the past 30 years, the Western Hemisphere witnessed the arrival of a number of unexpected and important arthropod-borne viruses (arboviruses): dengue trickled in with small outbreaks that became more aggressive in the 1990s,1 West Nile virus (WNV) emerged in 1999,2 chikungunya in 2013,3 and in 2015, Zika virus became a global health emergency.[4] Arboviruses are viruses transmitted by arthropods, predominantly mosquitoes and ticks, and are often maintained in complex zoonotic transmission cycles.[5] Arboviruses are normally maintained in wild animal reservoirs, such as nonhuman primates or birds, making elimination difficult and prediction of spillover to humans challenging.[6,7] As a consequence, effective allocation of public health resources is complicated and often reactive
Infected mosquito lags were short enough that skillful forecasts could still be generated for mosquito infection indicators, but the human West Nile virus (WNV) case lags were too great to support accurate forecasting in real time
During the past 30 years, the Western Hemisphere witnessed the arrival of a number of unexpected and important arthropod-borne viruses: dengue trickled in with small outbreaks that became more aggressive in the 1990s,1 West Nile virus (WNV) emerged in 1999,2 chikungunya in 2013,3 and in 2015, Zika virus became a global health emergency.[4]
Summary
During the past 30 years, the Western Hemisphere witnessed the arrival of a number of unexpected and important arthropod-borne viruses (arboviruses): dengue trickled in with small outbreaks that became more aggressive in the 1990s,1 West Nile virus (WNV) emerged in 1999,2 chikungunya in 2013,3 and in 2015, Zika virus became a global health emergency.[4] Arboviruses are viruses transmitted by arthropods, predominantly mosquitoes and ticks, and are often maintained in complex zoonotic transmission cycles.[5] Arboviruses are normally maintained in wild animal reservoirs, such as nonhuman primates or birds, making elimination difficult and prediction of spillover to humans challenging.[6,7] As a consequence, effective allocation of public health resources is complicated and often reactive. West Nile virus is the leading cause of domestically acquired arboviral disease and has produced the 3 largest arboviral neuroinvasive disease outbreaks ever recorded.[8] In response to the emergence of WNV in the Western Hemisphere, the US Congress provided funding to establish ArboNET, an electronic surveillance system for arboviral diseases in the United States, and to support surveillance activities in affected states and large cities. Surveillance consists of 2 distinct but complementary measures: (1) a network monitoring WNV activity in mosquito vectors and nonhuman vertebrates and (2) a passive system that records WNV human disease, which can be used to quantify disease burden and identify seasonal, geographic, and demographic patterns of morbidity and mortality in humans.[9]
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