Researchers say, the rate of American children being sickened by pesticides at school jumped 39% in four years, from 5.6 out of every million students in 1998 to 7.8 per million in 2002.

The number of children poisoned by pesticides at school has jumped in recent years, according to a new study that measured the casualties of organized spraying in and around classrooms.

Dr. Walter Alarcon of the National Institute for Occupational Safety and Health said that doesn’t count the untold number of children who may not know they were exposed to pesticides at school nor don’t suspect pesticides cause their sickness.

“Pesticide exposures at schools continue to produce acute illnesses among school employees and students in the United States, albeit mainly of low severity,” said Alarcon, whose findings appear in today’s Journal of the American Medical Association.

Using reports from three national toxic surveillance programs, Alarcon’s team tracked 2,593 people who got sick after being exposed to insecticides, disinfectants, bug repellents and weed killers at schools.

He added, “Little kids have very sensitive lungs and even very low levels of chemicals can irritate and inflame their airways” pesticide poisoning commonly goes undiagnosed or misdiagnosed, because symptoms resemble flu-like illnesses, pink eye or stomach problems.

In the Northeast U.S., pesticide-related illnesses spiked in 2000, rising from 5.4 cases per million students in 1998 to 10.4 cases. It’s unclear if that was due to bug spraying in the wake of the West Nile virus.

There are no federal rules limiting pesticide use in schools. But city public schools only use pesticides as a last resort, Education Department spokeswoman Margie Feinberg said.

If pesticides are going to be used, “schools must provide written notification to all parents, guardians and staff,” at least 48 hours before they are used, Feinberg said.