NAPERVILLE (CBS) — A west suburban Naperville man is the first reported human case of West Nile virus in DuPage County this year.

The man in his 50s was treated as an outpatient and his symptoms have improved, according to the DuPage County Health Department.

As of last Wednesday, a total of eight people in Illinois had contracted West Nile virus. Nobody has died, the Illinois Department of Public Health said.

Health officials say most people infected by the virus show no symptoms, but people over 50 or those suffering a chronic disease are at-risk for serious complications.

Residents should use insect repellent, empty any standing water outside and avoid outdoor activities between dusk and dawn when mosquitoes are the most active, officials said.