Are you involved with Legionella monitoring programs or Legionella outbreak control? Currently there are about 50 known species of Legionella and about 70 serotypes or serogroups that have been recognized to cause diseases in humans. The most common species of Legionella that causes Legionnaires’ disease is Legionella pneumophila serogroup 1.
Laboratory for Testing Legionella
Testing for the presence of Legionella bacteria is reliably accomplished by culture in an accredited laboratory using well-characterized and validated methods. Mold & Bacteria Consulting Laboratories (MBL) Inc., is accredited by the Canadian Association for Laboratory Accreditation (CALA) and also certified by the US Centers for Disease Control and Prevention (CDC) for Legionella testing. Through the Environmental Legionella Isolation Techniques Evaluation (ELITE) Program, CDC certifies labs that are able to find Legionella in a water sample by culture method. See MBL’s Legionella Certificate of Proficiency.
Occurrence of Legionella
The natural habitats of Legionella are environmental waters like lakes, streams and rivers. They thrive in warm waters. Legionella sp. may be isolated from:
- Surface water, mud and from thermally polluted lakes and stream.
- Hot water tanks, cooling towers, evaporative condensers, humidifiers, and holding tanks.
- Decorative fountains, ultrasonic mist machines, whirlpool bath.
- Spas, respiratory therapy equipment, showers, water faucets, technical-medical equipment.
- Fire sprinkler systems, safety showers, and industrial process equipment.
- Damp potting soil.
Sampling Procedure For Legionella
Water samples are the practical way to sample for Legionella. Legionella counts will be more accurate in water than air and testing will indicate the potential risk for exposure. When sampling for Legionella always use a sterile container containing sodium thiosulfate. Samples should be kept cool and overnighted to the lab for analyses. Samples should be received at the laboratory no later than 48 hours from sampling.
Non-Potable Systems – Cooling Towers And Evaporative Condensers.
Samples can be collected in a sterile 500 mL bottle containing sodium thiosulfate. When collecting from the reservoir the bottle should be inverted under the water and moved in a single direction. Try not to collect excess sediment in the water samples.
Decorative Fountains, Hot Tubs, Fire Sprinkler Systems, Cisterns, And Humidifiers
Samples should be collected in a 500 mL bottle containing sodium thiosulfate. Include water from the bottom and near the sides of the reservoir.
Potable Water Systems
Hot Water Systems. Two samples should be taken when sampling a hot water system. A pre flush sample and a post flush sample. When collecting the pre flush sample, turn the hot water tap on immediately collect the first 300 mL of water containing sodium thiosulfate. Sinks, showerheads, hoses, or bottom of hot water tank are all places samples can be taken. When collecting the post flush sample, allow the water to run for 1 full minute or until water sample is hot then collect sample in a 300 mL bottle containing sodium thiosulfate. By pulling two samples you can determine if the contamination is at the fixture or from the supplied water in the plumbing lines.
Cold Water Systems. Cold water systems can be analyzed by collecting the first draw sample. Drinking fountains, faucets and shower-heads are the appropriate outlets to sample. Collect 300 mL of water in sterile container containing sodium thiosulfate.
For testing Legionella in domestic waters such as drinking water, water coolers, chillers, eye washers etc, samples may be collected in sterile 1000 ml or 500 ml bottles with sodium thiosulfate. The 1000ml bottles are available from the lab upon request.
SWAB, Air, And Bulk
Swab sampling is a method recommended done alongside water samples. Bulk samples can be tested for Legionella. Often bulk samples are sludge from the bottom of a condensate pan scraped off a cooling coil. Samples should be collected in a sterile container, kept cool and transported to the laboratory within 24 hours of collection. Air samples can be collected using special Legionella media which can be ordered from the lab.
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