The surge in West Nile virus among mosquitoes in the city mirrors a broader increase across the country, according to the U.S. Centers for Disease Control and Prevention. Here are five key things to know about the West Nile virus and how the city combats it. The health department has conducted routine surveillance of mosquitoes to mitigate West Nile virus since it was first detected in the city in 1999. Then, they’re tested for West Nile virus. “Our spray criteria is two consecutive pools of West Nile virus, with high numbers of biting mosquitoes.