Legionella bacteria are the causal agents of Legionnaires disease, Pontiac fever, and related pulmonary illnesses. Although there are 39+ species, all capable of causing disease, over 85 percent of all recorded legionellosis cases have been caused by a single species, L. pneumophila. It has been estimated that up to five percent of the pneumonia cases that occur in the United States are actually caused by species of Legionella. Yet, perhaps as little as ten percent of these are correctly diagnosed and reported to the Centers for Disease Control. This high incidence of misdiagnosis has been attributed to failures of physicians to order the analytical test and/or from false negatives that are due to the insensitivity of the clinical test itself.
Low concentrations of the bacteria occur ubiquitously in soils, municipal water supplies, and particularly non-marine aqueous environments. Complete eradication of Legionella in water supplies is virtually impossible. Unfortunately, man-made water devices can create a niche in which the water borne organisms grow and attain numbers that would not normally be achieved in a natural environment. It is this explosion in numbers that allows Legionella to become an opportunistic pathogen.
An estimated 8,000 - 18,000 cases occur each year in the United States, 23% of these are nosocomial. The medical significance of the Legionella genus of bacteria was first recognized following a fatal outbreak of pneumonia among members of an American Legion convention in 1976. Since that time there have been many recorded outbreaks, as well as individual cases of legionellosis. In many respects Legionnaires Disease is a progeny of the technology age. Technology has facilitated many epidemics by providing the means for efficient transmission of the bacteria and has increased the number of susceptible hosts due to medical advancements.
Transmission of the bacteria is through man-made water devices that typically have warm water, suitable pH, stagnation followed by agitation, other living organisms present, and the presence of sediment. These water devices can include cooling towers, potable water systems, water systems in large buildings, whirlpool baths, respiratory care equipment, hot tubs, fountains, electric water heaters, showers and faucets. These sites are generally where "outbreaks" occur. Typically, under these scenarios there are a number of victims and fatalities occur. However, these "outbreaks" that garner so much media attention are only a small percentage of the estimated 8,000 - 18,000 cases of Legionnaires Disease that occur annually.
Examination of water samples is the most efficient microbiological method for identifying sources of Legionella bacteria. Of the available methods for its detection in environmental samples, the culture method remains the "gold standard". This method requires a ten (10) day incubation period. A molecular technique, polymerase chain reaction, or PCR for short, offers a very sensitive and specific method, and one that only requires a few hours to complete.
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 various buildings. Generally, any water source that may be aerosolized should be considered a potential source for the transmission of Legionella bacteria. Legionella can be found in municipal water supplies at low levels and the organism tends to colonize individual distribution systems and point of use devices. Legionella are thermotolerant and are found frequently in hot water systems. The bacteria are readily subject to desiccation and do not survive outside of a water source. Therefore, condensate collection devices from air conditioning equipment that frequently evaporate are not a likely source.
The investigator can collect two primary types of samples: water samples and swabs of point of use devices or system surfaces. The amount of water required by the laboratory for water samples depends upon the detection limit required by the investigator. Generally 100 milliliters of water is sufficient, unless a very low bacteria level is suspected and circumstances dictate concentration of the sample to obtain a detection limit of less than one organism per milliliter. If this is the case, a one-liter sample should be collected. The investigator should consult with the laboratory prior to collecting samples to determine which sample volume is more suitable. Swabs permit the sampling of biofilms, which frequently contain Legionella. These can be taken from various points within the plumbing system, from surfaces of water containing mechanical devices or from faucet aerators and showerheads. All samples should be transported to the laboratory in insulated coolers to protect against temperature extremes. Samples that cannot be delivered to the laboratory within 24 hours of collection should be refrigerated.
Water sampling is the most effective means of determining the presence of Legionella pneumophila. Air sampling is an insensitive method due to the fact that the life span of the bacterium is typically short lived in the aerosolized form.
The PCR method provides an extremely powerful screening tool for very rapidly detecting the bacterium in environmental samples, however it does not distinguish between living and dead cells, but unless the environment has been recently altered, such as with a biocide application, moderate to high populations of Legionella detected by PCR are usually indicative of an existing or potential future 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 requires confirmation via conventional culture techniques.
For more information on Legionella or sampling for Legionella, please contact Aerotech Laboratories at 800.651.4802, or visit www.aerotechlabs.com.