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Legionella water testing is necessary to determine if a water system is free of Legionella that could impact health. Testing will determine if protective measures are needed and to verify the efficacy of a water treatment system. Chemical water testing will only tell if a water treatment system is working and will not tell if the treatment is preventing the growth of Legionella.

Regulations and guidelines for Legionella testing of water systems.

Management of Legionella in water systems span from regulations that require some buildings to have water management plans that include monitoring of water samples for Legionella along with treatment, to no requirements. Assorted codes, standards, and guidance documents have been adopted related to Legionella control, elimination, and testing. Varied approaches have been developed to managing Legionella due to the absence of any federal law related to Legionella contamination of water. Currently there are no regulations to control and test for Legionella in water systems.

Federal Laws and Regulations

The Safe Drinking Water Act (SDWA) established a Maximum Contaminant Level Goal (which is a non-enforceable guideline) of zero Legionella in drinking water. This is consistent with the Centers for Disease Control and Prevention’s (CDC) position that there is no known safe level of Legionella.

Current control of organisms, such as norovirus, Giardia, and Cryptosporidium, using a multiple-barrier approach at the treatment plant continues to be effective. These pathogens are reduced through filtration and can be inactivated by the use of disinfection having the correct disinfectant and contact time. These methods, however, do not cover Legionella and some other environmental pathogens, which can grow in the piping system after treatment. A pathogenic cell can enter the distribution system which can grow in piping systems downstream of treatment. Legionella can grow where the disinfectant residual has decayed, and biofilms have developed.

Despite the water utilities’ maintenance of a distribution system disinfection residual, the responsibility for most public water systems ends at the meter. Water utilities have no control over how building owners maintain their plumbing systems.

Building owners can be required to comply with all the requirements that apply to a public water system, including bacteriological monitoring, control of disinfection byproducts, etc. at a cost to building owners. For many systems, disinfectants would only be on the hot-water system (where Legionella tends to thrive), which the EPA defines water “intended for human consumption” where water is used for drinking, bathing, showering, hand washing, food preparation, dishwashing and maintaining oral hygiene which all encompasses hot-water systems.

Currently buildings that have installed some type of secondary control for Legionella protection can be regulated as consecutive public water supplies, however there are no laws, regulation related to Legionella, only recommendations.

Local Regulations

Despite the lack of federal regulations or laws that could prevent the presence of Legionella in water systems, there are local and state regulations that attempt to do so. Plumbing and building codes can impact the control of Legionella and transmission in buildings, but primarily before occupancy.

Legionella Water Testing Standards

Currently there is a lack of standardization for the selection of sampling sites and the frequency of sampling. Guidelines on routine environmental testing for Legionella vary among different agencies, including the CDC, WHO, AIHA and ASHRAE.

  • AIHA recommends using validated laboratory methods to measure viable Legionella bacteria rather than surrogate indicators (e.g., chlorine residual) as part of routine assessments on a semi-annual frequency. AIHA also suggests that Legionella testing should be conducted for validation of the plan (i.e., confirming that the plan is effective at controlling the identified hazards), and as part of the outbreak investigation to determine the environmental source of the disease. However, they do not state frequency and how to test.
  • ASHRAE suggests that a team should be responsible for developing and implementing the building’s risk management plan for Legionella control and decide whether or not Legionella testing should be conducted. Criteria that can support such a decision include prior history of legionellosis, buildings that serve at-risk or immunocompromised populations, and the incorporation of control limits (i.e., defined values for chemical or physical parameters) into the risk management. However, they do not state frequency and how to test.
  • HSE advises that monthly Legionella testing be conducted in premise plumbing systems that provide treatment with biocides and where water is stored, or distribution temperatures are reduced. HSE provides some guidance on sampling locations in hot and cold-water systems. However, they do not state frequency and how to test.
  • VHA recommends routine environmental testing for Legionella in VHA facilities to validate the effectiveness of measures for Legionella However, they do not state frequency and how to test.
  • The Maryland Department of Health and Mental Hygiene (2000) recommends that water distribution systems within acute care hospitals be routinely cultured for Legionella at a facility-specific schedule determined by risk assessment. They also do not state frequency and how to test.

Despite the lack of guidance for environmental monitoring, both WHO and CDC acknowledge using Legionella testing as one way to verify and validate a Legionella management program.

If it is decided to conduct routine environmental testing for Legionella as part of a risk management program, it is suggested that a building-specific sampling plan be developed that specifies the location of sampling sites, the type of samples, the frequency of sampling, the sample collection method, and the sample analysis method. However, there is no consensus on how many and which types of samples to obtain (e.g., bulk water or biofilm), nor how often to perform the sampling in order to accurately assess the risk from Legionella.

CDC Routine Environmental Sampling

If environmental water sampling for Legionella is conducted, sampling should be part of a comprehensive water management program. Sampling frequency, location, and methodology is to be decided by the owner. Adjustments to the sampling method can be changed over time based on trend data and system changes. There is no known safe level of Legionella in building water systems. Cases of Legionnaires’ disease have been associated with very low levels of Legionella in building water systems. The intent of a water management program should be to manage building water systems to reduce the hazardous conditions that allow the Legionella to grow and spread to susceptible people.

Plumbing Codes

Plumbing codes dictate almost every facet of building plumbing design and installation. Some plumbing codes can be used to partially manage Legionella in building water systems. The National Standard Plumbing Code is adopted at the state level but are generally enforced at the county or municipal level by the relevant inspection entity. The plumbing code was not written with the goal of managing building water systems for Legionella.

ASHRAE 188 Standard

ASHRAE 188 standard takes an approach to managing Legionella in building water systems. ASHRAE recommends that parameters are monitored (not necessarily Legionella) to determine whether control measures are working. No recommendations for Legionella water testing are made.

Allegheny County Health Department Legionella Guidelines

Guidance documents state that all facilities should take a risk management approach regarding Legionella in their water systems. The Allegheny County Health Department guidance documents are the basis for the 30 percent positivity rule. However, the guidelines do not provide guidance for routine environmental testing for Legionella, but specifies the location of sampling sites, the type of samples, the frequency of sampling, the sample collection method, and the sample analysis method.

Guidelines for Interpretation of Legionella Monitoring Data

Currently there are no guidelines related to interpretation of Legionella water monitoring data. Guidelines for Legionella water monitoring as part of the building water management plan has not been recommended by the EPA or the CDC.

ASTM Procedure—Environmental Sampling for Legionella recommendations 

ASTM developed recommendations for environmental water testing for Legionella however it is only guidance. They estimate the number of samples to be collected based on a facility’s size and the number of water systems identified as potential Legionella sources. Recommendations for collecting water samples from: incoming water supplies; water storage tanks and hot water heaters; hot and cold-water faucets and shower heads; water-cooled heat-transfer equipment; and humidifiers, spas, decorative fountains, and other water systems that can harbor Legionella.

Sample Volume—Collect at least 10 to 100 mL of water from areas which may contain elevated concentrations of legionella. Collect more than 1 L of potable waters, which may contain lower concentrations of legionella. Use new containers or cleaned and sterilized ones to collect samples.

Recommended Legionella Testing

Given the lack of standards, regulations, and codes for Legionella water testing, it is up to the owner to develop a Legionella testing plan. Because the CDC position is that there is no known safe level of Legionella, zero Legionella in water is the goal.

The following is what a major medical institution has implemented for over 20 years.

  • The owner must determine location of sampling sites, the type of samples, the frequency of sampling, the sample collection method, and the sample analysis method.
  • The owner must work with a laboratory to determine the amount of sample water to be obtained related to culturing. Most laboratories require a minimum of 100 mL of water for water culturing.
  • Bulk water and not swabs for culturing. The culturing should be direct plate and concentrated plating. Direct plating is performed for Legionella, anything detected less than 1 CFU is reported as not detected (negative). Concentrated plating is also performed for Legionella, anything detected less than 1 CFU is reported as detected (positive). This is done because of a zero Legionella in water is the goal.
  • Frequency is recommended to be done quarterly and as needed.
  • Water sample bottles – 100 mL sterile bottles remained sealed and closed until ready to fill and reclosed immediately after sample collection. Collection of water at sinks, showers, and testing ports are first draw (testing collection of water soon as it flows).
  • Water sample bottle stopping residual biocide – sodium thiosulfate is in each sample bottle to neutralize residual chlorine and chlorine dioxide to prevent continued biocidal action during sample transport and storage.
  • Water sample locations – collect first draw water samples from city water, downstream of water treatment injection (if water treatment is utilized), hot water supply (downstream of hot water heater or convertor), hot water heater or convertor, hot water return, end of cold-water system, furthest sink and shower at end of piping to each patient unit.
  • Sample identification of each bottle – facility name; initials of person collecting sample; sampling site description; sampling date and time; sample identification number. Document all custody transfers and storage conditions from the time of sample collection to final disposition.
  • Review Legionella report from certified laboratory and forward to Infection Control, Facilities, Legionella task force with action recommendations for remediation and retesting if necessary.

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