West Nile virus (WNV) was first identified in Connecticut in 1999. To help learn more about the epidemiology of WNV in Connecticut, the Department of Public Health (DPH) in collaboration with other state agencies and local governments implemented surveillance systems in 2000. These surveillance systems included tracking WNV infections in humans, horses, wild birds, and mosquitoes.  During the first 5 years, it was determined that mosquito surveillance was the best sustainable indicator of potential human infections, therefore wild bird monitoring was discontinued in 2006. The DPH continues to monitor WNV in humans, horses, and mosquitoes.

The Connecticut Agricultural Experiment Station maintains 91 mosquito trap sites in 73 towns statewide. The trapping sites were selected based on habitat, proximity to residential areas, and historical findings. Results provide information on the numbers and types of mosquitoes present, as well as the rates of infection with WNV and other viruses that may have public health importance. The information obtained through surveillance helps guide statewide prevention and control measures.