The Southern Nevada Health District declared an outbreak of West Nile virus Aug. 22 after the virus sickened 28 people, the highest total since the state first detected the disease in 2004, according to ABC affiliate KTNV.
Seventeen of the 28 people infected had the more serious neuroinvasive form of the virus. The district's Mosquito Surveillance Program has found West Nile virus-positive mosquitoes in 39 unique ZIP codes.
The district has also seen a sharp increase in mosquitoes carrying West Nile or St. Louis encephalitis virus. About 19 percent of mosquitoes tested positive for either virus this season, compared to 0.1 percent last season.