Sampling for Legionella. (Technical Briefs).

Why Sample for Legionella?

Legionella pneumophila is a Gram-negative bacterium that is responsible for Legionnaires' disease and Pontiac fever. Transmission of the bacteria is through man-made water devices that typically have warm water, suitable pH, stagnation followed by agitation, the presence of other living organisms, and sediment. The water devices can include cooling towers, potable water systems, water systems in large buildings, whirlpool baths, respiratory care equipment, showers, and faucets.

Low concentrations of the bacteria occur ubiquitously in soils, municipal water supplies, and, particularly, nonmarine aqueous environments. Complete eradication of Legionella in water supplies is virtually impossible. Unfortunately, man-made water devices can create a niche in which the waterborne organisms grow and attain numbers that would not normally be achieved in a natural environment. It is the explosion in numbers that allows Legionella to become an opportunistic pathogen.

Water sampling is the most effective means of determining the presence of Legionella pneumophila. Air sampling is an insensitive method because the life span of the bacterium is typically short in the aerosolized form. Swab samples also can be collected from the biofilm around water sources but should follow initial water evaluation.

Equipment for Required Water Sampling

* Sterile 100 milliliter (mL) bottle with sodium thiosulfate preservative.

* Gloves.

Sampling Methods for Legionella in Water

1. Using the gloves, collect the water sample in the sterile bottle, filling to the line indicated on the jar. Do not overfill the jar, as doing so will rinse out the preservative.

2. Replace the cap and label the sample container appropriately

3. Ship samples on ice to the laboratory

Quality Control

The number and types of sites that should be tested must be determined on a case-by-case basis. Because of the diversity of plumbing and mechanical systems in buildings, more than one sample may be required from the suspect source. Generally, any water source that may be aerosolized should be considered a potential means for the transmission of the Legionella bacteria.

Multiple samples should be collected for comparison studies and include, at a minimum, a suspect sample and a sample from a nonsuspect source.

The culture method remains the gold standard for detecting Legionella from environmental sources. This technique, unfortunately, requires up to 10 days to complete, precious time that could be used to pinpoint sources of the bacteria and prevent additional exposures. A molecular technique, polymerase chain reaction (PCR for short), is a very sensitive method and requires only a few hours to complete.

The PCR method provides an extremely powerful screening tool for very rapidly detecting the bacterium in environmental samples. It doesn't distinguish between living and dead cells, but unless the environment has been recently altered, as with a biocide application, moderate to high populations of Legionella detected by PCR are usually indicative of an existing or potential problem. Therefore, the PCR method can rapidly identify potential sources, facilitating disinfection processes, and help to prevent further exposures. As this method does not determine viability of the bacteria, the PCR screen must be considered presumptive, and confirmation via conventional culture techniques is required.