ROCKVILLE, Md. (AP) - Montgomery County officials are warning parents that 12 students at four different schools have shown signs of whooping cough.

County health officials say there have been three confirmed cases of the respiratory disease and nine suspected cases. Health officials strongly urge parents to have their children vaccinated.

Whooping cough, or pertussis, is highly contagious. It begins with symptoms similar to a cold including coughs and runny noses. Then the cough worsens over weeks and becomes spasmodic.

School officials are urging parents to look for any symptoms.

Schools with confirmed or suspected cases of whooping cough include Robert Frost Middle School, Julius West Middle School, Cabin John Middle School and Cold Spring Elementary. Officials believe several of the children attended a summer camp together in Pennsylvania where they were exposed.