A recent rash of cryptosporidium outbreaks have hit swimming pools across the country, even one equipped with ultraviolet systems.

In Montgomery County, Pa., pools were shut down after 36 cases of crypto were confirmed. Most were linked to Spring Valley YMCA in Limerick, Pa., and a few cases were traced to the Sesame Rockwood Day Camp in Blue Bell. The Spring Valley Y had even recently installed an ultraviolet radiation system, which is designed to zap the parasite upon contact.

Experts say that UV systems only work if the water is clear. Any turbidity, cloudiness or algae prevents the UV from killing the parasite effectively. In addition, the pathogen can?t be killed until it goes through the system, which occurs about once every six hours, said Alison Osinski, Ph.D., president of Aquatic Consulting Services in San Diego.

?People in the pool at the time of the accident can get sick,? she said. And because the water turns over every six hours, ?for six hours, people were exposed.?

In Utah, approximately 80 cases of crypto were confirmed after swimming in area pools in several counties. Typically, about 40 Utah residents get infected with crypto each summer, but officials say the higher number of outbreaks occurred because more people visited pools during this summer?s heat wave.

About 23 cases of crypto were confirmed in Dubuque County, Iowa. Most were children using public pools, though some had recently swum in rivers as well.

Thirty-seven people reported being sick after swimming in the Okmulgee (Okla.) YMCA pool. Sixteen cases of cryptosporidium have been confirmed, and the health department traced the source back to the pool after eliminating other pools, the city water supply and exposure to child-care settings.

Another 18 were linked to two pools in Gillette, Wyo. The median age of those affected was 5 years old, and only four were older than 18.

Heavy rains caused cross-contamination of swimming pools and, as in Utah, above-average summer temperatures drew more people than normal, according to officials. But those variables alone aren?t to blame for the worsening problem, Osinski said.

?It?s an emerging pathogen,? she said, pointing out that the parasite once only attacked cows before it moved to humans. Each year, more outbreaks of crypto are occurring, but people also are more aware of it and reporting incidences more.

Cryptosporidium causes vomiting, diarrhea, fever, weight loss and other symptoms. It can be spread by fecal matter that is introduced into a recreational water setting; chlorine can take nearly a week to destroy it.