9 July 2019

Legionella: To Sample, or Not To Sample?...That is the Question

What's required and what is my sampling plan?

Perhaps the #1 question we are asked is: 

“Does ASHRAE 188-2018 (or the CMS Directive) require that I sample my water systems for Legionella?” 

The simple answer is no (not directly), and here’s why:  There is no known safe level of Legionella in a building water system.  Therefore, even a non-detect sample result is not necessarily “safe.” The reason why is because the life cycle of this organism, coupled with the stresses put on it via temperature, disinfectants, etc. found within building water systems, may cause it to enter a viable but non-culturable (VBNC) state. 

Culturing for the presence of Legionella and not detecting it should not lull a building owner into a false sense of security.  The reason for this is because these very same manmade plumbing systems might actually provide ideal environments for these bacteria to replicate, amplify, and colonize water systems possibly to alarmingly high levels at some time during the Legionella lifecycle.  Worse yet, cases of Legionnaires’ disease have even been associated with very low levels of Legionella in building water systems.  Therefore, as CDC, ASHRAE, CMS, and many others recommend, we need to manage our building water systems to reduce the hazardous conditions which allow Legionella to grow and spread to susceptible people.  We accomplish this via a Water Management Plan (WMP).

The water management program team should regularly monitor water quality parameters such as disinfectant and temperature levels which, if left unaddressed, could potentially encourage Legionella and/or other opportunistic waterborne pathogens to grow.  If, for example, the program team finds that a water parameter falls outside of their predetermined control limits, their next step would be to take corrective actions to get their building water conditions back to within desired ranges.  This could be a simple preventive measure such as flushing a stagnant or low-flow branch line or adjusting a domestic hot water heater set point, or it could be more corrective in nature like performing a system disinfection.

The general consensus is to not conduct random unsupervised environmental sampling in the absence of suspected or confirmed Legionnaires’ disease cases, unless it is part of an epidemiological investigation.  However, if environmental sampling for Legionella is utilized in the absence of suspected or confirmed facility-associated disease (e.g., for WMP validation purposes, etc.), it should never be performed in isolation, and before embarked upon, the program team must have an agreed upon sampling plan and appropriate response protocols established for systems and devices to be sampled.  Sampling plans are unique to each facility, and should consider such factors as:

  • Frequency of sampling (e.g., monthly, quarterly, etc.)
  • Location of sample points
  • Quantitative vs. qualitative response to test results
  • Environmental assessment of risk factors
  • Engineering factors of the systems to be tested
  • Building occupant risk; defined high risk populations
  • Past microbiological history of the systems
  • Correlations between clinical and environmental sample results
  • AHJ (Authority Having Jurisdiction) requirements for sampling, reporting, remediation, resampling, recordkeeping
  • Sampling method to be used

Whenever environmental sampling is used in the absence of disease, it should be performed by an accredited laboratory with demonstrated proficiency in the detection and enumeration of Legionella.

Chem-Aqua can assist in controlling your buildings waterborne pathogens risks, Water Management Plans, Sampling Plans, Risk Assessments, accredited third-party lab sampling, audits, supplemental and emergency disinfections, consultations, and more. Contact your Chem-Aqua Water Risk Management Service Group today at:  1-866-209-3373

Written by: Dominick Tuzzo

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