An Overview of Legionella Analyses
By Diane Miskowski, MPH
EMSL Analytical, Inc.
Background
The first recognized outbreak of Legionnnaires' Disease occurred in the US at the American Legion Convention in Philadelphia during the summer of 1976. There were several hundred people who were stricken. Thirty four people died from the disease. As a result of the efforts of the US Centers for Disease Control (CDC), this was the first time the bacteria was cultured and identified. Earlier outbreaks of the disease went undiagnosed. Since that time, there have been many identified outbreaks in this country and abroad prompting professional organizations and health departments worldwide to implement guidelines for diagnosing and reporting the disease, and monitoring the organism.
Transmission and Epidemiology
Ubiquitous in all aquatic environments, Legionella bacteria are found in groundwater as well as fresh and marine surface waters. The bacteria enter our plumbing systems, whirlpool spas, and cooling towers via these water sources. Unless control measures are conducted properly and routinely, the biofilm, scale, and corrosion that builds up over time in these systems will protect the organism and allow it to multiply.
Contaminated aerosolized water from cooling towers, whirlpool baths, nebulizers, faucets, and showerheads becomes airborne. When a susceptible host inhales the contaminated aerosol, legionellosis can occur. Aspiration of the contaminated water can also cause the disease. Legionellosis can cause two types of illness: 1. a severe form of pneumonia (Legionnaires' Disease) often accompanied by serious long term health effects, and 2. a mild flu-like illness called Pontiac Fever. Other infected organs, and asymptomatic infections may also occur.
Historically, risk factors for getting the disease included age, gender, compromised immune systems, and pre-existing medical conditions such as chronic obstructive pulmonary disease, cancer, and diabetes. Men over 65 years of age who were heavy smokers and drinkers were identified as being at greatest risk. While that is still true, recent research from Neil and Berkelman at Emory University has identified an abrupt increase in the incidence of Legionnaires' Disease in the US in all age groups in the last 20 years. This trend has also been noted internationally by other researchers. They have noted an overall increase in the disease among all people aged 45 to 64. Rates of disease in males still exceed the rates in females.
There also have been cases of the disease in healthy, younger people. Pre-mature, immuno-compromised, or ventilated neonates are at risk from hospital acquired infection. In addition cases have been reported in children aged 15-19 years old.
Although the disease is under-reported, travel (cruise ships), hotel, and resort related outbreaks are reported each year. These are mostly associated with the use of whirlpool spas and potable water. While community-acquired outbreaks involving cooling towers and whirlpool spas receive the most media attention, studies indicate that building potable water sources account for most of the infections. This is particularly true in hospitals and nursing homes where there are large numbers of immunosuppressed or critically ill people. For these reasons, many state health departments have guidelines that recommend routine monitoring for legionella in critical care hospitals and nursing homes. In 2008, the Veteran's Administration promulgated a directive which requires all VA hospitals and rehabilitation centers to implement monitoring for the bacteria in their potable water systems.
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Choosing Sampling Methods
Proper methods for collecting and analyzing samples are necessary to ensure defensible results. Since the bacteria in water are present in very low levels, 1000 mL potable water samples are recommended by the US Public Health Centers for Disease Control (CDC). This sample size allows for the bacteria in the water to be concentrated, allowing for better detection in potable water samples. . Many professional guidelines recommend semi-annual sampling for potable water sources.
In non-potable water sources such as cooling tower water, a 250 ml sample size is sufficient. Professional guidelines suggest these sources be monitored quarterly.
Sampling should be conducted in a way that maximizes recovery of the organism and mimics the route of exposure. Legionella samples should be collected wherever water aerosolization may occur.
Sampling aerosolized water alone, however, will likely miss the real source of the organism. This source is the biofilm or slime that is often found in our plumbing systems, cooling towers, and whirlpool baths.
A Legionella bacterium being ingested by a macrophage
