SPRINGFIELD, Massachusetts (AP) -- It has fouled carpeting, crawled over ceiling tiles and slimed books and bulletin boards in schools from Maine to Rhode Island.

An unprecedented mold outbreak, following the region's rainy, humid summer, has also delayed the opening of school for thousands of youngsters across New England and left some districts with six-figure cleanup bills.

"We are getting hundreds and hundreds of phone calls from schools all over the region," said Eugene Benoit, regional coordinator of indoor environment programs for the U.S. Environmental Protection Agency. Although he had no hard numbers, he said, "I haven't seen as many school closings or delays in openings in the 10 years I've been working with this."

More than 50 schools in Massachusetts alone reported mold problems after districts began reopening and cleaning their buildings in August, said Suzanne Condon, assistant commissioner for environmental health for the Massachusetts health department.

"Mold growth has been at a rate that we have never seen in history," Condon said.

The tiny spores, nurtured by a soggy and steamy July and August, also have vexed homes and other buildings across the Northeast. For classrooms left vacant for weeks, all the fungus needed to multiply into big problems was a leaky roof, a loose window, condensation from an air conditioning system or a section of shampooed rug left damp.

In healthy children, mold typically causes no more than hayfever-like symptoms in the eyes, nose and throat, but those with asthma and other breathing difficulties and immune system problems can be affected more severely, Condon said.

A spritz of household bleach or a good scrub with detergent will clean mold from hard surfaces, but cleaning other materials is a difficult, expensive task for districts already strapped for cash.

The Old Rochester School District in Mattapoisett spent $400,000 on around-the-clock work after mold got into the inner walls of an elementary school open just one year. Superintendent William Cooper said condensation around an air conditioning system is believed to have fostered the contamination, which forced the district to tear out some classroom walls to remove infested insulation.

The district did manage to start school on time -- unlike the Southbridge school district, where high school students were kept waiting for two weeks while the district replaced moldy desks, books and other material.