This dataset contains positive cases of West Nile virus found in humans by county of residence, 2006-present. Humans usually become infected with West Nile virus by being bitten by an infected mosquito. Viruses carried in the mosquito’s saliva enter the blood stream and local tissues where they infect immune cells. Most of the people who do become sick during a WNV infection develop what is referred to as “West Nile fever.” A small percentage of people will develop a much more serious illness called West Nile neuroinvasive disease (WNND). Positive cases in this dataset include both West Nile fever and West Nile neuroinvasive disease.