PROVO — In the realm of micro-organisms, cryptosporidia are the Navy Seals.

"They're tough," Ron Tobler, environmental health program manager for Utah County Health Department, said of the fecal-borne parasite responsible for more than 1,700 cases of cryptosporidosis in Utah since June. "They're intended to survive."

Guarded by a thick, outer shell, cryptosporidia, often referred to as crypto, can thrive in hostile conditions where other microbes succumb to the elements. In properly chlorinated water, Tobler said, most germs last only two minutes, but a crypto could conceivably survive up to six or seven days.

Crypto aren't just hard-shelled; their small size makes them difficult to filter, said Dr. Joseph Miner, director of the Utah County Health Department. An average crypto measures 4 microns in length, or about four-millionths of a meter, which enables the parasite to slip by most current pool filters, Miner said.

Swimmers can then accidentally swallow crypto-contaminated pool water and suffer severe symptoms, including diarrhea, stomach cramps, fever, nausea and vomiting — as occurred earlier this summer when so many people were infected by the parasite.

In response to the outbreak, public health officials banned children under age 5 from public swimming pools and required all pools to be flushed with super levels of chlorine, Miner said.

On Sept. 5, health officials lifted the ban for potty-trained toddlers and no longer require weekly hyper-chlorination. But Miner said they might have to resume those measures next spring to guard against another outbreak.

"We don't want it to explode to the point it was last year," he said.

In recent weeks, the county board of health has received many phone calls from businesses volunteering products to deal with crypto. While he's cautiously skeptical about such offers, Miner said he thinks the water recreation industry has room for improvement.

"There's always an opportunity to build a better mouse trap," he said. "This is an area that could definitely use some cost-effective means to better control this problem."

Representatives from Halosource, an antimicrobial company based in Bothell, Wash., suggested pool managers in Utah use a method called flocculation to filter crypto out of a pool system.

Jeff Williams, co-founder of Halosource and former professor of microbiology at Michigan State University, said the company developed SeaKlear PRS, a solution made up of two biopolymers. The solution causes crypto to adhere to one another and form large, stable lattices that can be flushed out through the pool filter system.

Tobler said he's heard of the method and "in principle it seems to work," but the system takes hours overnight to take effect.