Recreational water illnesses on the rise in the U.S.

Cases of recreational water illnesses (RWIs), which affect a person's stomach and intestines, skin or respiratory system, have risen over the past 20 years, according to the U.S. Centers for Disease Control and Prevention, with reports of of diarrhea-causing RWIs increasing by as much as 200 percent since 2004.

Daniel Lamptey, an infectious disease specialist at Mercy Medical Center, said the surge in RWIs is likely because more and more people are physically coming into contact with recreational water. He said five-star hotel pools aren't any safer than city-run neighborhood splash pads, if the amount of chlorine used to treat the water isn't adequate.

Swimming pools need a chlorine concentration of a least 1 parts per million and a pH between 7.2 to 7.8, according to the CDC.

"When people swim, they carry some of these organisms into the water. Occasionally, if the water is not treated correctly, the water already has these organisms," Lamptey explained. "When you get in and you happen to swallow the water, then it gets into your system."

Public health officials from 32 states and Puerto Rico reported 90 recreational water-associated outbreaks for 2011 and 2012, the most recent years data was available, to the CDC's Waterbourne Disease and Outbreak Surveillance System.

Sixty-nine of the outbreaks involved treated recreational water. Of those cases, 36 were caused by cryptosporidium, a protozoan parasite highly resistant to chlorine; and 21 were caused by escherichia coli, a rod-shaped bacterium. In total, 1,788 people were sicked, 95 were hospitalized and one person died.

"You don't need a large inoculum to contaminate the water and make people ill," Lamptey said of cryptosporidium, a leading cause of RWIs. "Just a small amount, once it gets into the water, it can make lots and lots of people ill.

Individuals infected with RWIs experience abdominal pain, diarrhea, nausea and vomiting. Lamptey said occasionally some people break out with a rash called folliculitis or develop ear or respiratory tract infections. While the illness can be treated with antibiotics, Lamptey said patients who are generally healthy can recover without them.

"It's the immunosuppressed people (those with HIV or who are receiving chemotherapy) who tend to have a difficult time," he said. "If you're not very ill, sometimes it's self-limiting and within a day or two you're fine."

Can you tell whether the water in a swimming pool is contaminated just by looking at it?

Lamptey said it's impossible to know for sure. If the water looks dirty, he advises against swimming or wading in it.

"People who have swimming pools know how to take care of them in terms of chlorine and how much to put in," he said. "Hotels and cruises know they have to be very careful so they don't lose their business if there's an outbreak. They pretty much do a good job of it."