A waterborne illness in swimming pools, lakes and water parks may have triggered the death of a Texas swimmer and sickened over 100 people.

The authorities are alarmed by the increase in cases. Dallas County Health and Human Services advised individuals with weakened immune systems to stay away from the bodies of water used for swimming or water-based recreations.

Experts say they don’t know the reason for the surge in the outbreaks of cryptosporidiosis, a parasitic disease which causes diarrhea, nausea, stomach cramps and vomiting. However, they draw attention to a range of presumptive factors, such as availability of a prescription drug to treat cryptosporidiosis and larger public awareness of the infection.

According to the Center for Disease Control and Prevention’s Web site, the disease can be spread through contaminated materials, water counting among them. It can survive for a long time and it presents resistance to chlorine disinfection found in swimming pools.

The number of reported cases in Texas has raised form 79 in 2003 to 237 in 2007. "Obviously this year it will be going way up," said Emily Palmer, spokeswoman for the Texas Department of State Health Service. "We'll have a big increase for '08,” she added.

Whereas in the Dallas-Fort Worth area 50 incidents have been reported since June, in Tarrant County 67 cases showed up, public health officials said.

The lakes and reservoirs in the city of Abilene, Texas, are monthly tested for crypto. According to Mike Michaud, manager Abilene's environmental laboratory, the tests performed to all water sources have come up clean.