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What's Living in Your Hot Tub?

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WebMD Health News

May 26, 2000 (Los Angeles) -- With summer just around the corner, your thoughts are probably turning to lazy days on the beach, getting some sun, and perhaps a nice twilight soak in the hot tub before barbecuing for dinner. But without proper disinfection of that hot tub, germs could multiply and ruin your summer overnight.

Organisms found in hot tubs can cause a wide variety of ailments, including skin rashes and infections, urinary tract infections, irritation of the digestive system, and even hepatitis and Legionnaires' disease. As long as you maintain your tub properly, there's little danger of catching something.

Bromine is the disinfectant most commonly used in hot tubs, and chlorine is also used, but in recent years manufacturers have developed a number of disinfecting systems that don't use either chemical. However, scientists at the University of Arizona in Tucson studied several of these systems and found that if you don't follow the instructions to the letter, germs can proliferate to dangerous levels. They presented their findings at a microbiology meeting here this week.

Lead author Pamela Watt, MS, and her colleagues conducted the study in two parts. In the first part, they used a "simulated" spa one-twelfth the size of an average real-life spa They compared the disinfecting abilities of bromine or ozone added to the tub's circulation system to enzyme or bromine tablets added to the water directly. They heated the water first, added the disinfectant, and then added two kinds of bacteria associated with skin infections or fecal contamination. After 30 minutes, the investigators took water samples to measure bacterial growth, or lack thereof. Bromine and chlorine were both effective at holding down bacterial growth, with bromine added to the generating system having a slight edge after 30 minutes. Neither ozone alone nor the enzyme had much of an effect.

In the second phase of the study, Watt and her colleagues tested disinfecting systems in real hot tubs under real-life conditions: two people sitting in the tub for 30 minutes at least four times in one week. This time they compared a generated ozone system to a silver ion cartridge and a silver ion cartridge with a chemical known as MPS added. In that portion of the study, only the silver ion cartridge plus MPS was better than ozone at discouraging bacterial growth.

"Basically the take-home message is, if you are going to use ozone in your spa, you must use chlorine or bromine also," says Watt, a research specialist in the department of soil, water, and environmental science at the University of Arizona. To be effective, she says, there must be a residue of disinfectant in the water at all times. "Ozone is a wonderful disinfectant, but it does not maintain a residual level," she tells WebMD. It simply does not last long enough in the water or on the surface of the tub to have an ongoing effect.

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