Legionella sampling in building water systems
IRIS microbiology team · CDC ELITE, ISO 11731 · 14:40
Cooling towers, potable loops and point-of-use fixtures. Bottle choice, volume, first-draw versus flushed, and recording temperature and chlorine at the tap.
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Legionella results take 8 to 14 days depending on the method, so a resample costs you real time. Collect it right the first time.
Confirm the method first
Decide before you sample whether you need culture, Legiolert, or both.
- Culture (ISO 11731) recovers total Legionella species. It is required wherever a rule names Legionella culture, such as New York State and NYC cooling towers.
- IDEXX Legiolert detects L. pneumophila only. It suits water management plan verification and post-remediation checks, but does not replace a required culture.
If you are unsure which applies, contact the lab before you sample.
Collecting
- Use the sterile sodium thiosulfate bottles the lab provides.
- Cooling towers: sample the basin, away from the biocide injection point.
- Potable and hot water: take a first draw. Do not flush and do not remove the aerator.
- Leave 1 to 2 cm of headspace in each bottle.
Shipping
Ship overnight with the COC inside the package. Kits include a prepaid FedEx overnight label. Analysis begins on the day the lab receives the samples.
Turnaround and units
| Method | Detects | Reported as | Turnaround |
|---|---|---|---|
| Culture, ISO 11731 | Total Legionella species | CFU/mL | 10 to 14 days |
| IDEXX Legiolert | L. pneumophila only | MPN/100 mL | 8 to 10 days (7-day incubation) |
Watch the units: 1 CFU/mL equals 100 CFU/100 mL. Convert before comparing a result with any CFU/mL threshold.
Serogroup typing is available with culture as a priced add-on. Rush options are available, so contact the lab if you are up against a deadline.
Download the Legionella COC (PDF).
Chain of custody
Pick the form that matches your test.
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