Hardest hit appears to be Clermont County, where there are 51 cases so far this year compared to 11 in all of 2003. Most of the cases have been in school-age children.

Hamilton County reported 25 cases by the end of August compared to a total of six last year.

Public health officials say this amount of activity is not alarming - the bacteria-borne disease is known to attack at different rates in different years. Just across the river in Northern Kentucky, only five cases have been reported all year.

But parents should be on the alert nonetheless.

The Milford School District in Clermont County put a notice on its Web site this week. "We have not had any active cases yet, but we want parents to know that what starts out sounding like a normal cough from a cold or allergy could actually be something more than that," said Milford school nurse Laurie Roessler.

The disease can be spread much like the common cold and causes prolonged coughing spells, difficulty breathing, hoarseness, hives and paleness. In infants, the illness can be so bad that it is hard for them to eat, drink or breathe.

Whooping cough is treated with antibiotics, and children with the illness are generally asked to stay home from school for five days.

Pediatricians routinely immunize infants against whooping cough, giving them a shot in combination with vaccines for diphtheria and tetanus. But the effectiveness of the whooping cough vaccine is known to wane, leaving some teenagers and adults vulnerable.

"We think that is what's going on," Clermont County Health Commissioner Janet Rickabaugh said.

Rickabaugh said cases began showing up in May. Two other clusters appeared in June-July and in late August. The clusters appear to be linked because of common interactions, she said.

Greater Cincinnati was hit with a whooping cough epidemic in 1993. Hundreds of cases were reported and entire classes of schoolchildren and large groups of employees were given shots to slow the disease.

Overall, between 5,000 and 7,000 cases are reported in the United States each year, according to the federal Centers for Disease Control and Prevention.

Thirteen children died in the United States last year from the disease. Most deaths occur among unvaccinated children.

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E-mail mleingang@enquirer.com