Legionella Testing

Legionella Tesing is the first step in Legionella PreventionLegionella testing is the only way to determine if a water source is contaminated with the bacteria and is one of the many important steps in Legionella prevention. The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) published ANSI/ASHRAE Standard 188-2015, Legionellosis: Risk Management for Building Water Systems in June of 2015 and is considered by many to be the definitive guideline for preventing legionella contamination. In their Guideline 12-2000: Minimizing the Risk of Legionellosis Associated with Building Water Systems, ASHRAE suggests that culturing for legionella is appropriate if carried out for a specific purpose, such as:

  1. Verifying the effectiveness of a water treatment program
  2. Tracing the source of a Legionellosis outbreak
  3. Evaluating the potential source of amplification and/or transmission at a facility
  4. Verifying that a disinfection procedure has been effective

Heterotrophic Plate Count Test

Heterotrophic plate count (HPC) testing, otherwise known as a dipslide test, is not an effective indicator of Legionella contamination. There are approximately 50 known species and 70 serogroups of Legionella that have been identified. HPC testing has a long history of use in water microbiology and will show if there is overall biological activity in a body of water; however, even in circumstances where a body of water has extremely high biological activity, it would require Legionella specific testing to determine if there was active Legionella bacteria serogroups in the water source.

Methods of Legionella Testing

There are many methods of Legionella testing; however, the following are the most popular:

  1. Cultured Samples – In this method water samples are cultured on a buffered charcoal yeast extract (BCYE) culture growth medium. Preliminary culture results typically require three to five days for confirmation. Confirmation of culture results may take additional time because some strains of the bacteria take 10 to 14 days to form visible colonies. Cultured samples may be analyzed to identify specific serogroups. There is strong evidence of a causal relationship when the same serogroup and subtype of an organism is isolated from a patient and a water source.
  2. Direct Fluorescence Antibody (DFA) – The number of Legionella organisms in a water sample can also be determined via direct fluorescence antibody (DFA) conjugate tests that stain the organism with a fluorescent dye. While this testing method can produce a result in as little as one to two days, a potential drawback to the DFA test is that it is unable to distinguish between live and dead bacteria and may have some cross-reactivity with other bacteria; and so the potential exists for both false-positive and false-negative results.
  3. DNA Amplification – This is a relatively new method for rapid, specific detection of Legionella bacteria that is becoming increasingly popular. It utilizes a polymerase chain reaction (PCR) process to amplify and then detect portions of DNA that is unique to Legionella. DNA Amplification can produce results in just one day.

Standardization of Testing

Legionella bacteria live in a wide variety of freshwater habitats and they can be difficult to isolate when testing. Culture and enumeration of Legionella from environmental sources involves several steps including concentration of the bacteria, resuspension, selective pre-treatments, and the use of complex media. The Centers for Disease Control and Prevention created the ELITE Program as a way for laboratories to test their Legionella isolation techniques against standardized samples. ELITE is an acronym for “Environmental Legionella Isolation Techniques Evaluation.” ELITE Certified Labs are sent a panel of test samples twice per year.  Labs that correctly identify Legionella from the test samples in two consecutive panels receive a certificate of proficiency and are listed among the CDCs ELITE Members.

A cultured sample analyzed by a CDC Elite lab is currently the “method of choice” in the United States.

Sampling Recommendations

The most important aspect of Legionella test sample is consistency. Test samples should be taken in the same place, in the same way, every time.

  1. Cooling Tower Water – It is recommended that cooling tower water samples be collected directly from the tower basin at the furthest most point away from the make-up-water. The sample should be free of sediment. The tablet included in most sample bottles is intended to stay in the bottle is meant to counteract and neutralize any existing halogen in the water during sampling. Once the sample is collected, secure the bottle and shake the sample for a few seconds to help dissolve the tablet. This collection method is appropriate for decorative fountains and hot tubs.
  1. Potable Water – For water collection, turn on hot water & immediately fill the sample bottle. If one exists, take care not to lose the tablet from the bottle during sampling. Once the sample is collected, secure the lid and shake the sample for a few seconds to dissolve the tablet.

For swab collections, remove aerator if present. Moisten the faucet by turning on the hot water for a short time. Insert the swab into faucet opening rotating two times against the inner surfaces. Collect a small amount of warm water from the faucet in the collection tube. Replace swab in transport tube and seal tube.

For a showerhead, rotate swab over entire surface of the showerhead at least two times. Collect a small amount of warm water from the faucet in the collection tube. Replace swab in transport tube and seal tube.

  1. Hot Water Storage Tank – Open the drain valve at the base of the heater or storage tank and immediately collect the flowing water into the sample collection bottle. Allow the water to continue to drain for 30 seconds to flush out sediment within the drainpipe. Collect another sample into a second sample bottle. Submit both samples to the lab labeled “immediate” and “post flush.” Swabs are not considered an appropriate sample for hot water tanks.

Once sample has been taken, it should not be overly handled and should be shipped to an approved lab immediately. Please note: Since many labs are closed on the weekends, it is practical to take samples earlier in the week so that they are delivered in a timely manner.

Legionella Testing Services

At Clarity Water Technologies, we offer Legionella testing services with every water treatment contract we write. This is especially important in states like New York, where Legionella testing is required every 90-days while a cooling tower is in operation. If you are trying to comply with the New York City Cooling Tower Testing Requirements, we can help.

Please keep in mind that Legionella test results only represent the counts at the time that the sample was collected and that testing is not a substitute for proper maintenance and water treatment practices.