Where Should I Sample for Legionella?

  • 3 March 2020
  • Author: Dominick Tuzzo
  • Number of views: 3625

“Which devices, fixtures, and/or systems within my building are at highest risk for harboring Legionella?” 

Should your Water Management Plan (WMP) Program Team decide to utilize environmental water sampling to validate the effectiveness of the WMP, ANSI/ASHRAE 188-2018 advises that these tests should be performed by a laboratory accredited to a nationally or internationally recognized standard (e.g., ISO/IEC 17025:2017), with Legionella included in the laboratory’s scope of accreditation.

Before environmental sampling is undertaken, a Sampling Plan should be formulated.  This plan should list the devices and Points of Use (POUs) to be sampled, at what frequency sampling will be performed, what the acceptable control limits will be, and what the response protocol will be for any sample result(s) falling outside of the previously-established control limits. 

Sample Point Examples

High risk devices (so classified because they aerosolize water into their surrounding environments) include, but are not limited to, the following:

  • Cooling Towers, Fluid Coolers, Air Washers
  • Decorative/Ornamental Fountains
  • Misters, Atomizers, Cold water humidifiers
  • Industrial water spray systems using domestic (non-sterile) water as their source
  • Spas/Hot Tubs
  • Car washes
  • Pot washers / Cart washers / Decontamination wash wands

Plumbing fixtures to consider include:

  • Electronic and manual sink faucets
  • Aerators
  • Flow restrictors
  • Showerheads and shower wands
  • Plumbed Eyewash stations and Emergency Showers
  • Domestic Hot & Cold water storage tanks
  • Medical devices which use plumbed domestic water

Systems within the building to consider sampling include:

  • Cold water POE (Point of Entry) into the building
  • Online DHW (Domestic Hot Water) heaters
  • HWR (Hot Water Return) where equipped
  • Any high risk devices listed above
  • Industrial or process water systems which aerosolize water

Sampling Plan Strategy

A sampling plan strategy for potable (domestic) water systems in healthcare facilities has been promulgated by the New York State Department of Health Bureau of Water Supply Protection.  This guidance can help you formulate your own building sampling plan.  Their recommended sampling strategy includes:

  • A sample of the inlet cold water supply at the first available tap
  • One sample from the return piping of the circulated potable water heating system(s)
  • One sample from the outlet of the heating system(s)
  • At least three samples should be collected from each floor.  This is normally done as follows:
    • Tap closest to first delivery of hot water from the riser
    • One sample from the middle of the system
    • One sample from the last outlet before the water returns to the piping that conveys water back to the heater
    • During an investigation of illness, samples from locations that housed ill patients/residents will be needed
  • Risers sometimes feed multiple circulation loops with each loop providing water to a group of rooms.  Several sample locations should be designated for each loop.
  • One additional random sample should be collected from each floor when wings have extensive lengths of piping and complex paths
  • They suggest surface samples (swabs) be performed at locations representing the middle or end of the hot water lines on each floor during your initial building assessment.
  • Because cold water distribution systems can also harbor Legionella, especially if the water is allowed to become stagnant and/or tepid, these potentially problematic locations should be sampled to determine the presence of Legionella and if so, design and/or operational changes may need to be implemented to correct the problem.

For assistance in controlling your buildings waterborne pathogens risks, WMP’s, Sampling Plans, Risk Assessments, accredited third-party lab sampling, audits, supplemental and emergency disinfections, consultations, or any questions, contact your Chem-Aqua Water Risk Management Service Group today at:  1-866-209-3373

Written by:  Dominick Tuzzo

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