About 400 new cases of whooping cough have been confirmed in Minnesota in the past month, pushing the state's total to nearly 2,400 infections this year -- highest since vaccines were introduced in the 1950s.

With the start of the school year approaching, more cases may pop up, said Cynthia Kenyon, a senior epidemiologist at the Minnesota Department of Health. "Sometimes, we see a lot more activity when school starts," she said.

Among children age 7 to 12, one-fourth of the cases affected children who were under- or unvaccinated. So state health officials are recommending that parents have their children vaccinated, especially in areas with a high rate of disease, including the seven-county metro area, Wright County, Albert Lea and Rochester. Adults in close contact with infants and kids -- like teachers, coaches, health care professionals, day-care providers and family members -- should get booster shots, they said.

Whooping cough, or pertussis, creeps up every two to five years naturally, which could account for some of the new cases. In Minnesota cases typically range from 200 to 1,500 a year.

The disease is spread through droplets coughed by infected people and often begins with coldlike symptoms. It usually can be treated effectively with antibiotics. Infants, however, may not cough and instead suffer episodes of apnea and difficulty breathing.

High vaccination rates can create "herd immunity,'' which prevents illnesses from jumping from person to person and is especially important to protect individuals who are not vaccinated, including babies. When vaccination rates drop, the barrier becomes porous, making it easier for illnesses to spread.

Getting vaccinated "is part of being in a community and protecting your neighbors and the most vulnerable," Kenyon said.

Daniela Hernandez • 612-673-4088