Three confirmed cases of whooping cough and nine suspected cases have been reported by Montgomery County at four schools, according to officials and a letter that went home to parents.

Whooping cough, or pertussis, is highly contagious and begins with mild, coldlike symptoms, including coughs and runny noses. The initial symptoms usually appear seven to 10 days after exposure.

The cough usually gets worse over subsequent weeks and becomes spasmodic. It may be followed by a whooping sound that gives the disease its name.

Pertussis is spread through coughs or sneezes and may also be spread through sharing food or eating utensils. In the letter that was sent home, officials said it is important that students who are ill remain at home and stay away from other people, especially infants and young children.

The illness is caused by bacteria and treated with antibiotics. Public health officials strongly urge parents to have their children vaccinated as infants, and a booster is recommended at age 11 or 12.

Montgomery County warns about whooping cough in schools

The letter

Montgomery County health officials warned parents at four public schools that there have been reported cases of whooping cough among students who apparently attended the same summer camp. Read the letter.

The schools with confirmed or suspected cases are Robert Frost Middle, Julius West Middle, Cabin John Middle and Cold Spring Elementary.

Health officials believe that several children who attended a Pennsylvania summer camp were exposed to pertussis. It was not immediately clear how many students who went to the camp or attend the four schools have been vaccinated.

Parents were asked to watch their children for symptoms and notify their children’s primary-care provider quickly if any are seen.

In a provisional report for 2013, federal health officials said 24,231 cases of pertussis had been reported in the United States. The report said 196 cases had been reported in Maryland, about 3.3 cases for every 100,000 residents. Nine deaths were listed in the United States, all in infants younger than 3 months old.