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Hot tubs that are not properly operated and maintained can provide an ideal environment for spreading Legionella, the bacteria that causes Legionnaires' disease and Pontiac fever. The phrase "hot tubs" in this document includes hot tubs, whirlpool spas, and hydrotherapy spas.

Failing to regularly scrub hot tub surfaces to remove biofilm, the slime layer that protects Legionella from disinfectants, and failing to maintain adequate disinfectant levels promotes Legionella growth. Hot tub users can be infected with Legionella when they breathe in tiny water droplets that contain Legionella.

CDC has not made any recommendations regarding routine laboratory testing for Legionella, because proper hot tub maintenance and operation should prevent the growth of Legionella. However, if cases of Legionnaires' disease or Pontiac fever are linked to a hot tub, it is important to take samples for laboratory testing and then disinfect the hot tub to prevent others from being infected.

While no scientific studies have been conducted to determine the best way to disinfect a hot tub contaminated with Legionella, CDC recommends these best practices based on the scientific information that is currently available:

  1. Close the hot tub to bathers immediately
  2. Shut down the hydrotherapy jets and circulation pumps, but do not drain the water.
  3. Contact your state or local public health agency
  4. for information about laboratory testing for Legionella. If the health department determines that laboratory testing is needed, water and biofilm samples should be taken from the tub, hydrotherapy jets, drain, and filters/filter media to test for Legionella by culture before taking the steps below. Sampling and laboratory testing are complicated and should always be done in collaboration with your state or local public health agency and a laboratory with Legionella testing expertise. A list of CDC-certified Legionella-testing laboratories can be found at https://wwwn.cdc.gov/elite/Public/ MemberList.aspx.
  5. After samples have been taken; it is not necessary to wait for laboratory test results. However, the hot tub should not be re-opened to bathers until all test results are negative for Legionella.
  6. Drain all water from the hot tub. Dispose of the water to waste or as directed by the local regulatory authority.
  7. Scrub VIGOROUSLY all hot tub surfaces, skimming devices, and circulation components with free chlorine at a minimum concentration of 5 parts per million (ppm) to remove any biofilm or slime. After scrubbing, rinse the tub with clean water and flush to waste.
  8. Replace filters (for cartridge or diatomaceous earth filters) or filter media (for sand filters). Bag these and dispose as normal solid waste.
  • Inspect the hot tub thoroughly for any broken or poorly functioning components such as valves, sensors, tubing, or disinfectant feeders. Make any needed repairs.
  • Refill the hot tub with clean water.
  • Hyperchlorinate using 20 ppm free chlorine. a.) Keep the hydrotherapy jets off and let the hyperchlorinated water circulate for 1 hour in all of the components of the hot tub including the compensation/surge tank, filter housing, and piping. b.) Turn on the hydrotherapy jets to circulate the hyperchlorinated water for 9 additional hours. Ensure that 20 ppm of free chlorine is maintained in the system for the entire 10 hours.
  • Flush the entire system to remove the hyperchlorinated water from all equipment prior to repeat sampling.
  • Take repeat samples for culture-based laboratory testing to confirm that Legionella has been eliminated. Water and biofilm samples should be taken from the tub, hydrotherapy jets, drain, filters/filter media, and any part of the hot tub that originally tested positive for Legionella.
  • Keep the hot tub closed to bathers until this repeat testing has confirmed the elimination of Legionella. If laboratory testing is positive for Legionella, repeat steps 4-11 until all testing is negative for Legionella. When all tests are negative, the hot tub can be re-opened to bathers. Ensure that halogen (chlorine or bromine) and pH levels meet local and state standards before re-opening the hot tub to bathers.
  • Maintain water quality according to local and state standards. Continued Legionella testing may be considered on a case-by- case basis to ensure complete elimination of Legionella.