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What's Living in Your Hot Tub?

From the WebMD Archives

May 26, 2000 (Los Angeles) -- With summer just around the corner, yourthoughts are probably turning to lazy days on the beach, getting some sun, andperhaps a nice twilight soak in the hot tub before barbecuing for dinner. Butwithout proper disinfection of that hot tub, germs could multiply and ruin yoursummer overnight.

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

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

Lead author Pamela Watt, MS, and her colleagues conducted the study in twoparts. In the first part, they used a "simulated" spa one-twelfth thesize of an average real-life spa They compared the disinfecting abilities ofbromine or ozone added to the tub's circulation system to enzyme or brominetablets added to the water directly. They heated the water first, added thedisinfectant, and then added two kinds of bacteria associated with skininfections or fecal contamination. After 30 minutes, the investigators tookwater samples to measure bacterial growth, or lack thereof. Bromine andchlorine were both effective at holding down bacterial growth, with bromineadded to the generating system having a slight edge after 30 minutes. Neitherozone alone nor the enzyme had much of an effect.

In the second phase of the study, Watt and her colleagues testeddisinfecting systems in real hot tubs under real-life conditions: two peoplesitting in the tub for 30 minutes at least four times in one week. This timethey compared a generated ozone system to a silver ion cartridge and a silverion 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 discouragingbacterial growth.

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

"If you buy a system [with instructions to add something] you have toadd it," she says. "If you want to maintain a spa with clean water,make sure you follow the instructions. Consumers need to be wary ofchlorine-free products and they need to [add these chemicals] every day. If youskip even one day you could have [a problem]." Swimming pools present lessof a risk because the colder water is less inviting to bacterial growth.

"As long as you can smell the bromine in the water, you're OK," saysmicrobiologist Jon J. Calomiris, PhD. Calomiris was not involved in thesestudies but conducted his own studies of bromine disinfectants in hot tubswhile a graduate student at Johns Hopkins University in Baltimore. Herecommends adding bromine in a concentration of five milligrams per liter ofwater in the tub and warns consumers to heat the water before adding thechemical, as disinfection works better at higher temperatures. He tells WebMDthat there are no known side effects of bromine in these amounts and that itis, in fact, less irritating than chlorine.

If you use someone else's spa, both Watt and Calomiris warn against standingaround in your bathing suit afterward. That gives any bacteria trapped betweenyou and your suit even more of an opportunity to come into contact with yourskin. "The next day you'll have a rash that looks like the bathingsuit," says Calomiris. Watt recommends getting out of your suit as soon aspossible and bathing after using the spa.

Vital Information:

  • Without proper disinfection, germs can grow in hot tubs and cause skinrashes, infections, digestive problems, and even hepatitis and Legionnaires'disease.
  • Researchers note when using ozone for disinfection, chlorine or brominealso should be used, because they linger in the water and help prevent germgrowth between cleanings.
  • A researcher adds that heating the water and using five milligrams ofbromine per liter of water are effective methods of controlling germs. Hottubbers also should change out of their wet bathing suits quickly so germsdon't have extra time against the skin to cause problems.