Legionella Sampling

How Legionella Water Sampling Actually Works

Reliable Legionella results start long before the lab. American Analytical Testing Services (AATLS) is an ISO/IEC 17025-accredited, CDC ELITE-certified laboratory in Tucson, Arizona, and this page walks through how Legionella samples are planned, collected, preserved, shipped, and analyzed under ASHRAE 188 and CMS requirements. If you need the program-level overview — what Legionella is and why to test — see our Legionella testing services page.

1. Designing the sampling plan (ASHRAE 188)

A defensible Legionella sampling plan is risk-based. Under ASHRAE 188 and the facility’s Water Management Program, sample points are chosen to represent the system, not to hit an arbitrary count: incoming supply, the hot- and cold-water loop extremities, the points furthest from the heater, low-flow and dead-leg fixtures, and high-risk devices such as showers, ice machines, decorative fountains, and cooling towers. We help map control locations to control limits so each result ties back to a documented point in your plan.

2. Sample types — water vs. biofilm/swab

Two evidence types tell different stories. First-draw (pre-flush) water samples capture what a user would actually be exposed to at the outlet, while post-flush samples reflect conditions deeper in the distribution system. Biofilm swab samples taken from inside faucet aerators, shower heads, tank walls, and cooling-tower basins often detect colonization that bulk water misses, because Legionella shelters in biofilm. A typical investigation collects both a water aliquot and a swab from the same fixture.

3. Collection mechanics, neutralizer, and hold times

Samples are collected into sterile containers (commonly 250–1,000 mL bottles for water; sterile swabs in transport media for surfaces). For any chlorinated or disinfected system, bottles must contain sodium thiosulfate to neutralize residual chlorine at the moment of collection — without it, the disinfectant keeps killing Legionella in transit and under-reports the true count. Samples are kept at ambient-to-cool temperature (protected from freezing and from heat), and analysis should begin within the recommended hold time — ideally within 24–48 hours of collection — to preserve viable organisms.

4. Chain of custody and overnight shipping to Tucson

Every sample ships with a completed chain-of-custody form documenting site, point ID, date/time, collector, residual disinfectant, and temperature. We recommend overnight courier to our Tucson laboratory so samples arrive inside hold time. Call 928-985-9399 and we will send pre-labeled, neutralizer-dosed sampling kits so field crews collect correctly the first time.

5. Analysis options: CDC ELITE culture vs. qPCR

AATLS offers two complementary methods. CDC ELITE Legionella culture is the compliance gold standard: it recovers viable organisms, speciates, and quantifies in CFU, with a 10–14 day turnaround — this is the result regulators, CMS surveyors, and ASHRAE 188 programs expect. qPCR rapid screening detects Legionella DNA in roughly a day and is ideal for fast situational awareness, outbreak triage, or screening many points before committing to culture — with the caveat that it cannot by itself distinguish viable from non-viable cells. Many facilities screen by qPCR, then confirm and quantify positives by culture.

6. Clearance sampling and routine frequency

After remediation (thermal or chemical disinfection), post-remediation clearance sampling verifies the corrective action worked before the system returns to normal service — clearance is confirmed by culture, not screening. For ongoing programs, healthcare facilities and cooling towers are commonly sampled on a quarterly cadence under their ASHRAE 188 Water Management Program, with frequency adjusted to risk and findings. We help build the schedule and turn each round into audit-ready documentation.

Ready to set up a Legionella sampling plan or order kits? Contact AATLS in Tucson at 928-985-9399 or [email protected].