Potential contamination sources include:

• Water-cooled, heat-transfer systems;
• Domestic water systems;
• Humidifiers and misters; and
• Any water sources maintained above 20°C (68°F) and that could be aerosolized.

Focus inspection efforts in areas where the workers with confirmed Legionellosis were most likely exposed.

Assume all potential contamination sources are contaminated and treat them accordingly. This includes hot and cold domestic water systems, cooling towers and humidifiers.

Workers performing water system sampling must wear appropriate personal protective equipment (PPE), as described on the Control and Prevention page.

Before flushing or disinfecting water in these suspected sources, ensure water system samples are collected for analysis. These samples are important in confirming that a Legionella hazard exists in the workplace, and, if so, what water systems or parts of water systems are contaminated. Depending on outbreak, these samples also can help determine:

1. The predominant L. pneumophila strains (i.e., serogroups and subtypes) in each water source.
2. The amount or concentration of Legionella in the system, often measured in colony forming units (CFU) per milliliter (ml) or other water unit.
3. Whether the the serogroup and subtype of bacteria found in individuals with Legionellosis match the bacteria found in a water source (a strong evidence supporting an associated epidemiological link). This information helps identify Legionellosis outbreak sources if the L. pneumophila serogroup is identified in the afflicted worker population.

Consider seeking additional expertise from environmental health and safety professionals and/or the local or state health department. Most employers are not equipped to take their own water system samples. The Hazard Recognition page provides additional information and resources on sampling protocols.

Ensure water system sampling, testing, disinfection, and other outbreak response activities are conducted safely and in accordance with currently accepted procedures. Always follow the hierarchy of controls—starting with elimination/substitution and engineering controls before implementing administrative controls and safe work practices and personal protective equipment (PPE)—to prevent or reduce worker exposures to Legionella during these activities. The following section discusses control measures and other actions for responding to outbreaks related to several different types of water systems.

Controlling exposure to Legionella during an outbreak might not require facility shutdown. Temporary provisions to isolate the affected water system can allow work to continue, and may include:

• Supplying bottled water for drinking instead of drinking from the domestic cold water system.
• Shutting down water heaters to eliminate access to hot water in the domestic system.
• Using temporary cooling towers.
• Using portable heaters, air conditioners, and fans instead of the contaminated HVAC system.

Building maintenance, engineering staff, or a third-party expert consultant who has working knowledge about a water system's design and current operation can explain how the system operates and the proper procedure for a controlled shutdown.

If the hazard assessment indicates there may be Legionella in the system, it is critical to take control actions immediately, even if the sampling results are negative. Water system sampling can produce false negatives and the sampling protocol can miss a contaminated portion within the system. Just because Legionella was not found during pre sampling does not ensure that the facility’s water system will remain negative.

Once samples are analyzed, the laboratory will provide colony forming units (CFU) counts per either volume or area for the water and/or biofilm samples. Results indicating Legionella is present are the most reliable and can lead to definitive statements about the source. However, negative results are not reliable since there is a high probability for Legionella to die, thus not counted, in the sampling process. A negative Legionella result from a water system sample should not lead to the assumption that the water system is no longer a potential source for Legionella in the workplace. The analyzing laboratory may also provide CFU counts per either volume or area for water and/or biofilm samples.

Most outbreaks from cooling towers and evaporative condensers are associated with high Legionella concentrations, at least 1,000 CFU/mL or more in the implicated source.¹ Typical Legionella concentrations average 160 CFU/mL (range <1 to 1,500) in a potable water system associated with outbreaks. Legionella concentrations as few as 10 CFU/mL in fogger reservoir water may have caused disease in people in immediate direct contact with the mist.

The expandable boxes below contain operating system-specific water treatment protocols for potential contamination sources following inspection and water system sampling.

Cooling Towers and Evaporative Condensers

Use the decontamination procedure below to treat all cooling towers or evaporative condensers that have been tested and found to be contaminated with Legionella at detectable levels, or when Legionella contamination is suspected.

Step 1. Clean and disinfect the entire cooling system, including attached chillers and/or storage tanks (sumps), following the Cooling Technology Institute's emergency disinfection procedure:

• Remove heat load from the cooling system, if possible.
• Shut off fans associated with the cooling equipment.
• Shut off the system blowdown.
• Keep make-up water valves open and operating.
• Close building air intake vents in the cooling tower’s vicinity (especially those downwind) until after the decontamination procedure is complete.
• Continue to operate the recirculating water pumps.
• Add a biocide sufficient to achieve free residual halogen at 25 to 50 ppm.
• Add an appropriate bio-dispersant (and antifoam, if needed).
• Maintain 10 ppm free residual halogen for 24 hours. Add more biocide, as needed, to maintain the 10 ppm residual.
• Monitor the system pH. Since the halogen disinfection rate slows at higher pH values, add acid, if needed, and/or reduce cycles to achieve and maintain a pH less than 8.0 (for chlorine-based biocides) or 8.5 (for bromine-based biocides).
• Drain the system to a sanitary sewer. If the unit discharges to a surface water source under a permit, dehalogenation is necessary prior to any discharges.
• Refill the system and repeat from beginning of Step 1.
• Inspect after the second drain-off. If a biofilm is evident, repeat the procedure.
• When no biofilm is obvious, mechanically clean the tower fill, tower supports, cell partitions and sump.
• Refill and recharge the system to achieve a 10 ppm free halogen residual. Hold this residual for one hour and then drain the system until no turbidity exists.
• Refill the system and charge with appropriate corrosion and deposit control chemicals, re-establish normal biocontrol residuals and put the cooling tower back into service.

Step 2. Identify and eliminate all water leaks into the cooling water system.

Step 3. Institute maintenance to ensure continued safe and proper operation, as follows:

• Inspect equipment monthly.
• Drain and clean quarterly.
• Treat circulating water to control microorganisms, scale, and corrosion. This should include systematically using biocides and rust inhibitors, preferably supplied by continuous feed, and monthly microbiologic analysis to ensure bacteria control.
• Document operation and maintenance in a log or maintenance records book.

If any water system sample contains Legionella at 10 or more CFU/mL, take immediate steps to clean the system. These steps may include more frequent biocide application or increased biocide concentration, pH adjustment, additional “shock” water treatments, or any other action to reduce Legionella levels. Take new water system samples and begin the cooling system water testing schedule again.

Domestic Hot Water Systems

Use the following decontamination procedure to treat all domestic hot water systems either tested and found contaminated with Legionella at detectable levels or when Legionella contamination is suspected.

Step 1. Disinfect the system using any effective chemical, thermal, or other water treatment method. For example:

• Heat the water to at least 70°C (158°F) and maintain this temperature for a 24-hour minimum. While maintaining the temperature at 70°C (158°F), continuously flush each faucet in the system with hot water for 20 minutes.
• Use an accepted chemical disinfectant such as chlorine or an acceptable biocide treatment to decontaminate the water system. Thoroughly flush the water system after treatment to remove all corrosive and possibly hazardous chemicals.
• Follow any other technique with demonstrated effectiveness and safety.

Step 2. Maintain domestic water heaters at 60°C (140°F) minimum and water delivered at the faucet at 50°C (122°F) minimum. Where maintaining these temperatures is not feasible, control Legionella growth with a safe and effective alternative method (See the Control and Prevention page).

Domestic Cold Water Systems

Use the following decontamination procedure if cold water systems are found contaminated with Legionella at detectable levels or when Legionella contamination is suspected.

Step 1. Clean and 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 (see the Control and Prevention page).
• Use any other technology demonstrated as safe and effective.

Step 2. Ensure that cold water systems are maintained so that conditions do not promote Legionella growth. Maintain temperatures at 20°C (68°F) and keep residual chlorine in the 1-2 ppm range. However, this chlorination level may also corrode metal pipes and containers.

Step 3. Flush all cold water outlets and fountains for four minutes, 12 hours before re-entry.

HVAC Air Distribution Systems

The most probable condition where a Legionellosis outbreak might link directly with an air handling system would include Legionella-contaminated water continuously entering the system and aerosolizing before delivery to workers or building occupants. Air handling systems may be ruled out as sources after the following:

• Inspect the entire air distribution system, including return and exhaust systems, for visible water accumulation (e.g., leaks, stagnant water, water damage).
• Eliminate all water leaks and remove any standing water found in the system. Replace or eliminate any water-damaged insulation in the system.
• Operate the HVAC system using 100-percent outside air for eight hours before returning the building to normal operation.

There is no reliable detection of Legionella in the air, and Legionella can live only in water. If the ducts are dry, they cannot serve as a Legionella contamination source.

After returning the building to normal operation, keep outside air supply rates as high as possible for one month. At a minimum, operate the system to meet the outdoor air requirements from American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) Standard 62.1, Ventilation for Acceptable Indoor Air Quality.

Humidifiers

Cold water humidifiers require rigorous maintenance to ensure that the water source does not contribute to potential microbe problems. Since humidifiers discharge into HVAC air distribution systems, inspect for standing water and treat according to the HVAC Air Distribution Systems protocol found on the Control and Prevention page.

Use the following decontamination procedure if Legionella contamination is suspected in water in humidifiers.

Step 1. Disinfect water in piping or reservoirs feeding the humidifier with chlorine or other effective biocides.

Step 2. Implement an adequate maintenance program to reduce Legionella growth. Ensure that water storage temperatures are kept above or below the 20° to 50°C (68° - 122°F) range, and keep the system clean.

Step 3. Before using the humidifier, flush the piping and/or reservoir thoroughly to remove biocides.