WAUKEGAN, Ill. (AP) — Lake County health officials are warning of an outbreak of whooping cough.

There have been 138 confirmed cases in the county and surrounding areas as of Wednesday, the highest number in five years.

READ MORE: Pair Charged In Murder Of 8-Year-Old Melissa Ortega Denied Bail; Accused Teen Gunman Committed Three Previous Carjackings, Prosecutors Say

Symptoms include a long-lasting, severe cough that’s usually worse at night. Officials say people who have such symptoms should see a doctor, because over-the-counter medicines are ineffective.

Whooping cough is highly contagious and can last for several months. Vaccines can prevent it, but a booster may be needed.

READ MORE: Chicago Weather Alert: Heavy Lake Effect Snow Possible Through Tomorrow Morning

Health officials say the disease can be fatal to infants, so it is important that they’re immunized.

Lake County Health Department Executive Director Irene Pierce says cases also are being reported among children and young teens — including some who were previously vaccinated.

MORE NEWS: Bears Reportedly Hiring Colts Defensive Coordinator Matt Eberflus As New Head Coach

(TM and © Copyright 2010 The Associated Press. All Rights Reserved. This material may not be published, broadcast, rewritten or redistributed.)