Legionella Testing / Biosafety Training

Legionella Detection and Sampling Methods

Legionella Detection and Sampling Methods

Legionella Testing Laboratory Procedures

An outbreak of Legionella bacteria can occur when water in plumbing lines or mechanical equipment is not tested regularly or properly. When testing water sources for legionella, there are a variety of detection and sampling methods that can be used by a legionella testing laboratory. Each test method has different effectiveness when determining whether the bacteria are in a water sample.

One detection method a legionella testing laboratory can perform is the culture method. The legionella culture method is the approach for detecting legionella colonies on BCYE agar. The culture method takes ten days to complete, which is a loss of valuable time needed to prevent exposures and identify the source. The culture method for environmental water samples is often not accurate because legionella colonies on BCYE agar media are often overgrown or inhibited by competing microbial flora that mask the presence of legionella colonies, particularly with water samples taken from warm water-containing mechanical equipment exposed to the environment such as fountains, cooling towers, and saunas. Another testing method is the PCR method, or polymerase chain reaction. PCR is a technique that only takes a few hours to complete and can be a useful method to screen drinking water samples. The downside to this method is that it does not work well with water samples exposed to the environment because dirt and debris cause a high background that masks the presence of legionella in the water sample. The original “gold standard” method to quantitate legionella in both drinking water and environmental samples is the direct fluorescent antibody (DFA) method developed by CDC in 1978. The DFA method has become more specific and sensitive by using monoclonal fluorescent antibody specific for several serogroups of L. pneumophila and several other legionella species that cause Legionnaires’ disease. The DFA method requires expertise which many legionella testing laboratories do not have.

When a legionella testing laboratory is called in to sample water, there are two main methods they can use: swab and bottle. Swab sampling involves collecting a surface sample with a sterile swab. Swab sampling is not frequently used since the spread of legionella is by individual bacteria floating in an aerosol or spray and swab samples do not permit quantitation of legionella in the water producing an aerosol or spray. Bottle bulk water sampling is the most common method. Bottle sampling consists of collecting water from potable water fixtures or from warm-water-containing mechanical equipment. Bulk water sampling permits the quantitation of the numbers of legionella per specific volume of water.

How A Legionella Testing Laboratory Uses Bottle Sampling

This sampling procedure is based on information about how people acquire Legionnaires’ disease. This procedure offers no guarantee that personnel will avoid contamination by Legionella. Wear a HEPA or N-95 respirator and gloves during sampling if you suspect heavy Legionella contamination.

Please note:  Do not put dirt or debris into the sample bottle. These recommendations are based on over 36-years of field testing experience by our GTS Legionella Water Testing Company.

Sample Procedure:

  1. Before going to get the sample, use a ballpoint pen to print on the sample bottle label; the source of the sample and the date the sample was taken.
  2. If sampling a domestic water system (water line, shower head, hot water heater, heat exchanger, sink, fountain, spa, humidifier, etc.), obtain a first draw sample from the system and follow steps 4, 5, 6, and 7 below.
  3. If sampling a cooling tower or evaporative condenser, obtain a sample from the tower bulk water circulating line and follow steps 4, 5, 6, and 7 below.  This sample should represent water in the tower drift. Do not sample dirt from the bottom of the sump or biofilm material.
  4. Make sure the 4-ounce (120 ml) bottle we supply you is full of water, tighten the cap securely.
  5. As soon as possible, rinse off the outside of the sample bottle, put the sample label on the bottle and wash your hands with soap and water.
  6. Put the labeled bottle(s) in a return sample box along with our chain of custody document with your institution’s name, contact person name, email address, telephone number and billing/charge information
  7. Return sample bottle(s) at ambient temperature as soon as possible to our GTS legionella testing laboratory.