PORTLAND – After causing outbreaks at Portland and Biddeford high schools earlier this year, whooping cough has reappeared among students attending summer athletic camps.

Dr. Dora Anne Mills, director of Maine’s Bureau of Health, said health officials had hoped the summer vacation would reduce the number of new cases.

“What we didn’t take into account was that a number of high schools have summer athletic camps and adolescents still see each other all summer long,” she said.

Whooping cough, or pertussis, is rarely fatal to older children and adults but can kill unvaccinated infants. Mills said she plans to send a letter alerting high school coaches to the bacterial infection because several infants have caught pertussis from adolescent family members in the last month.

Once viewed as a danger to infants, whooping cough has made a comeback nationally, increasingly among older children. Maine has already posted 70 lab-confirmed cases in the first seven months of this year, compared to 90 for all of 2003.

About 60 percent of this year’s cases involved children between 11 and 18 years of age, Mills said. Before 2003, more than 50 percent of diagnosed cases were children younger than 5.

State officials are waiting to see if the Food and Drug Administration will approve booster shots for older children and have urged parents to make sure children receive all appropriate vaccinations.

The vaccine is not approved for children over 7, and immunity is believed to wear off five to 10 years after the last booster shot.

It is important to identify those who are sick because it spreads quickly, health officials said.

About 15 teachers and students at Portland’s Cheverus High School were diagnosed and treated for pertussis this year. Up to 70 people were treated with antibiotics after close contact with those infected.

Several hundred people throughout southern Maine have received similar treatment since the spring, Mills said.

Symptoms of whooping cough at first resemble a cold – a runny nose, a cough – before escalating into fits of staccato-like coughing that sometimes end in a high-pitched “whoop.”

“You start getting spasms and some people ultimately can vomit with all that coughing,” said Dr. Jennifer Friedman, a family practitioner in Gorham. “It’s much more than your everyday kind of a cough.”

New cases this summer in Bangor have led state authorities to believe the infection is moving north. With school starting in about a month, Mills said she expects to see a resurgence of cases in more parts of the state.