Surveillance Data

Environmental Health Services conducts surveillance activities for West Nile virus (WNV) seasonally, from May through October, by operating with partner agencies 42 mosquito collection traps located throughout DuPage County. These traps are designed to capture the Culex species of mosquitoes, which is the primary transmitter of WNV in our area. After collection, the mosquitoes are tested for the presence of the virus to predict the risk of human exposure.

In addition to the Health Department, other public and private agencies conduct mosquito testing in the County, including: City of Naperville, Clarke Environmental Mosquito Management, Inc., Illinois Department of Public Health and Forest Preserve District of DuPage County. The location and most recent test results can be found on the Surveillance Maps page a few days after the statistics below are updated.

Current Activity Levels 

The chart below summarizes the current WNV activity level based on surveillance testing by all agencies this mosquito season.

DuPage County West Nile Virus Surveillance Data 2021Week:30
7/25 - 7/31
Year to Date
Mosquitoes Tested1,66515,317
WNV Total Tests38391
WNV Positive Tests715
Positive Mosquito Pool Rate Percent (%)18%4%
Reported Human Cases00
Communities with Human WNV Cases00
Personal Protection IndexRisk Level 1


Bird Reporting

Mosquitoes are infected with WNV after biting infected birds, which are the host or reservoir of the virus in the environment. The presence of dead birds can also be an indicator that the virus is present in an area. Dead bird sightings can be reported by using the reporting tool on the Tick and Dead Bird Report page.

Birds that are reported should be dead no more than 48 hours and have no other obvious causes of death. Within a few hours of your report, you may be contacted by our staff to arrange for pick-up of the bird for further testing. Otherwise, the dead bird can be disposed of by double-bagging and placing in your household trash.

Human Cases

Human cases of WNV are monitored by our Communicable Disease/Epidemiology Unit, which receives reports of WNV cases from local doctors, hospitals and laboratories. Human case information will be listed in the surveillance chart above, as cases are reported.