More than 200 people in July were sickened by a recreational water illness outbreak at a Pennsylvania university swimming pool that appears to have multiple contaminants.

Visitors to the Graham Natatorium Pool at West Chester University in West Chester, Pa., reported cases of diarrhea, nausea and vomiting shortly after swimming. Early test samples revealednorovirus traced back to the pool, causing the facility to be shut down immediately on July 10. Since then,cryptosporidium and one case ofgiardia also have been identified in stool samples.

The Chester County Health Department issued a health alert requiring all pool managers in the county to treat their pools forcrypto by superchlorinating and backwashing. It also requires the managers to ask bathers and staff, before entering the pool, if they had any symptoms of diarrhea or vomiting within the past two weeks. In addition, all swimmers must shower before entering, and any unusual illnesses must be reported.

The health department is awaiting reports from investigations and private providers, said Betsy Walls, bureau director for personal health services. She?s already given the go-ahead for the pool to be reopened, but none of its staffers have been released to return to work.

This outbreak is similar to others seen across the country, said Alison Osinski, Ph.D., president of Aquatic Consulting Services in San Diego. ?Having a secondary water treatment, a good UV treatment, would probably kill off [the disease] before it infects too many people,? she noted.

It can take nearly a week for chlorine to destroycrypto;giardia takes at least 24 hours. Norovirus, usually found in hotels and cruise ships, can be contained within an hour by chlorine.