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Legionnaires' Disease

Section II:C-2. Domestic Cold-Water Systems

Cold-water Systems Domestic cold-water systems are not a major site for Legionnaires' disease bacteria (LDB) growth. However, elevated levels of LDB have been measured in ice machines in hospitals. Cold-water lines near heat sources in the units are believed to have allowed the bacteria to multiply. Dental water lines have been recognized as sources of water contaminated with high concentrations of microorganisms including LDB. However, an increased risk of disease among dental staff or patients has not been demonstrated.

Control Strategy:

Top Which cold-water systems have been recognized as a source of LDB contamination?
Cold-Water Systems
Fig.1: Dental water lines may be a source of contamination
Under most circumstances, evacuation of the building is not recommended. However, with confirmation of an outbreak individuals with compromised health conditions should be considered for removal from the implicated building. Individuals at high risk for contracting the disease include:
  • Ice machines in hospitals supplied by cold-water lines near heat sources that promote LDB growth.

  • Water tanks that allow water to remain uncirculated for long periods also can promote bacterial growth.

  • Cross-contamination of a domestic cold-water system with another system should always be suspected of promoting bacterial growth.

  • Emergency water systems such as fire sprinkling systems, safety showers, and eye wash stations are other domestic cold-water sources from which LDB have been cultured. These systems experience little water flow and can be subject to periods of elevated temperatures. In addition, operation of these devices will aerosolize water. For these reasons, emergency water systems should be considered potential sources of LDB, although no documented cases of legionellosis have been associated with these sources.

  • Operating conditions for dental water lines are especially appropriate for LDB proliferation because the water is stagnant a majority of the time, the narrow plastic tubing encourages bio-film formation, and the water temperature is usually 20C (68 F) or higher -- some systems maintain water at 37C (98F). 

    • Filtration of water at the point of use with replaceable, in-line, Food and Drug Administration (FDA) approved, 0.22-micrometer pore size filters is recommended for minimizing risk to patients and staff in dental facilities.


Back to TopHow do I maintain a cold-water system?
Flush Showers
Fig.2: Flush safety showers monthly.
Maintaining cold-water lines below 68F (20C) will limit the potential for bacterial growth. Other methods to consider include the following:
  • Maintain residual chlorine levels as per local authorities recommendation.

  • Eliminate "dead leg" sections or frequently flush taps to drain stagnant areas to limit growth of the organism.

  • Eliminate or design stagnant tanks to reduce storage time to one day or less.

  • Cover cold-water lines to prevent contamination and protect them from temperature extremes.

  • Protect all connections to process water with a plumbing code-approved device such as a back-flow preventer or air gap.

  • Flush safety showers and emergency eye wash stations at least once a month.


Back to TopHow often to test cold-water systems for LDB following identification of contamination?
Outbreak Protocol:

When treatment steps are successfully completed, return the water system to normal operation but test it for LDB according to the following schedule:
  1. Weekly for the first month after resumption of operation.

  2. Every two weeks for the next two months.

  3. Monthly for the next three months.

  4. If tests fail, repeat the disinfection procedure and restart the test program.


Back to TopHow do I collect cold-water samples?
Collect water samples to determine potential contamination, as outlined above. Note: It is important not to flush the outlet before taking a sample because the end section of the water system may be a source of contamination.

Water Sampling Protocol: Sampling information specific to cold-water systems is provided below. For more information about water sampling, please refer to Section II:E. Water Sampling Guidelines.
  • Sample the incoming water supply if the plumbing provides access.

  • Sample cold water tanks and reservoirs if any.

  • Sample faucets and showerheads throughout the facility, for example, those nearest, intermediate, and most distant from storage tanks and connections with municipal water supplies.

  • If a biocide is used, follow the manufacturer's instructions for proper neutralization.
Interpretation Guidelines:
  • The OSHA suggested guideline for LDB in domestic cold-water systems is less than 10 CFU per milliliter.

    • If LDB concentrations are below 10 CFU per milliliter and no LDB were detected in swab or other samples, no further monitoring for LDB is necessary. Continue the maintenance program as long as the system is in use.

    • If water concentrations exceed 10 CFU per milliliter or LDB were detected in other samples, take steps to identify the source of contamination or amplification and treat the system
      See How to treat a contaminated water system.

      • Sample the water system monthly until the source of contamination is identified and adequately treated. Once LDB concentrations remain below 10 CFU for a tree-month period, sampling may be stopped.

Back to TopHow to treat a contaminated cold-water system
Flush Outlets
Fig.4: Flush cold-water outlets.
Cold-water systems have no provision for heating water, therefore, disinfection cannot be by heat treatment. The treatment procedure below should be used if cold-water systems are shown to contain measurable LDB or are assumed to be contaminated based on epidemiological evidence.
  1. Clean then disinfect all cold water systems including storage tanks, drinking fountains, water lines, and water outlets, as follows:

    • Use an accepted chemical disinfectant such as chlorine or other acceptable biocide and follow the manufacturer's instructions.

    • Use other technology that has been shown to be safe and effective.

  2. If the cold-water lines have significant contamination, hyper-chlorination can eradicate LDB.

    • Raise the level of free chlorine to 20-50 mg/L and maintain this concentration for one hour at 50 mg/L or for two hours at 20 mg/L.

    • Faucets are then allowed to run until the odor of chlorine is present, and the water is allowed to remain for approximately two hours.

  3. Flush all cold-water outlets and fountains for four minutes to remove disinfectant, at least twelve hours before re-use.

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