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Legionella Bacteria Sampling

Legionella Sampling (Water or Swab)


  • Routine monitoring: To detect and quantify the level of culturable Legionella species present in the environmental sample.
  • Case investigation: To recover an isolate from the environment for comparison with clinical isolates.
  • Post remediation: To determine efficacy of remedial measures.

Advantages and Disadvantages

  • Advantages
    • No major sampling equipment is necessary to sample for Legionella species.
    • Culturable samples allow for serotyping of Legionella isolates, which can aid in investigations.
  • Disadvantages
    • Culturable samples require up to two weeks of incubation to grow and isolate some Legionella species.


  • Clean collection bottles with neutralizer (e.g. thiosulfate) for halogenated water. For routine monitoring 250 ml sample size is sufficient; for recovery of isolates for case investigations multiple samples per outlet or larger sample volumes (1 liter) are recommended.
  • Non-cotton tip sterile swab.

Sampling Protocols

  • Legionella do not survive in dry environments—Legionella species require moist environments, so samples should not be collected from sites that demonstrate periodic drying. This is very important when considering where to sample. Sampling for Legionella species typically involves collecting water samples and swabs from potential sources. Collection sites range from taps and faucets to water storage reservoirs. Ideally, samples should be taken from a water source or other moist environment. Please remember that it is important not to flush water outlets before taking a sample for Legionella analysis because the end section of the water system may be a contaminated site.
  • Common locations where Legionella can be found include cooling towers, evaporative condensers, fluid coolers that use evaporation to dissipate heat and, domestic hot water systems with water heaters that operate below 60°C (140°F) and deliver water to taps below 50°C (122°F).
  • For potable water collect 250 ml of water for routine monitoring and if possible larger volumes or several samples for isolate recovery in case investigations. For non-potable water, a minimum of 100 ml is appropriate.
  • Data collected from swab samples are qualitative if no area is given, and quantitative if an area is given. Air sampling is not often conducted since it generally results in a low recovery of Legionella species from the environment.


  • Samples must be shipped to the Legionella testing laboratory for overnight delivery as it is recommended to begin analysis within 24 hours from sampling. Shipping temperatures should be kept between 2°C and 18°C. During hot weather it is recommended to add cold packs or ice in a cooler containing the sample containers.