What did a decade of West Nile virus surveillance in the U.S. reveal?

West Nile virus is a mosquito-borne illness that can cause serious neurological problems. A new surveillance summary from health officials looks back at ten years of data, from 2009 through 2018, to describe the virus's activity across the country. This kind of report doesn't test a new drug or vaccine; instead, it's a routine accounting of where cases were reported and when they occurred. It's a tool for tracking the virus's presence over time. The report describes the surveillance data that was collected. It doesn't make new claims about how many people got sick or compare it to other time periods. This is simply a descriptive look at what was recorded during that decade, which helps experts understand the virus's patterns.