SPRINGFIELD — The Illinois Department of Public Health is warning of a marked increase in pertussis, or whooping cough cases, primarily in Chicago and surrounding counties.

Statewide, there have been 1,149 cases reported, with most in Cook, McHenry, DuPage and Lake counties.

Early symptoms of pertussis are similar to a common cold and include a runny nose, sneezing, low-grade fever and mild, occasional cough. But the cough becomes more severe, and after a couple of weeks, it continues with bursts of rapid, high-pitched "whoop" coughs, according to public health.

Pertussis is treated with antibiotics. Anyone who has been in close contact with someone with confirmed or suspected pertussis is urged to seek medical attention immediately.

Pertussis is most risky to infants under two months old, who are too young to be vaccinated. That's why it's important for family members and caregivers coming into contact with infants to be vaccinated against the disease, according to Brandon Meline, director of maternal and child health at the Champaign-Urbana Public Health District.

There have been six confirmed cases of pertussis in Champaign County this year. There have been seven confirmed and probable cases in Douglas County and one confirmed case reported by the Piatt-DeWitt Bi-County Health Department, according to state health officials.