Legionella: An Emerging Environmental Health Concern

Legionella are small gram-negative rod-shaped bacteria, with over 50 individual species known. The majority of human infections are caused by the species Legionella pneumophila, which was first discovered following a pneumonia outbreak at the 1976 Convention of the American Legion in Philadelphia. However, 18 species have been known to cause cause human disease.

There are two forms of the disease: Pontiac fever and the more severe Legionnaires’ Disease. Pontiac Fever is a less severe form of legionellosis, which is characterized by flu-like symptoms (fever, chills, headache, and muscle pain) lasting 2-5 days. Legionnaires’ disease is a potentially fatal illness (fatality rate 5% to 30%) involving pneumonia lasting 2-10 days, with frequent long-term health effects. It is difficult to distinguish this disease from other pneumonias. Early diagnosis and treatment are extremely important and treatment consists of intravenous administration of antibiotics.

Legionella are most commonly found in water, including groundwater, fresh and marine surface waters, and potable (treated) water. The bacteria enter our plumbing systems, whirlpool spas, and cooling towers via these water sources. In addition, these bacteria have been found in water distribution systems of hospitals, hotels, clubs, public buildings, homes, and factories. These bacteria may be transported from potable water to air by faucets, showerheads, cooling towers, and nebulizers. 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.

Legionella are transmitted directly from the environment to humans. There is no evidence of human-to-human or animal-to-human transmission of these bacteria. Potable water is the most important source of Legionella and inhalation is the most important route of exposure. Humans may inhale contaminated aerosols from cooling towers (very important source), whirlpool baths, nebulizers, faucets, and showerheads. One may also aspirate small amounts of contaminated drinking water. No vaccine is available to prevent infection.

The general population (healthy individuals) is fairly resistant to infection. Historically, risk factors for getting the disease included age, gender (males), compromised immune systems, and pre-existing medical conditions such as chronic obstructive pulmonary disease, cancer, diabetes, and the use of immunosuppressive drugs. Men over 65 years of age who are heavy smokers and drinkers have been identified as being at greatest risk. While this is still true, recent research has identified an abrupt increase in the incidence of the disease in all age groups in the last 20 years. This may be because of the increase in the use of immunosuppressive drugs.

Personal safety and precautions should be observed during all sampling. Environmental samples should be collected from areas where water flows. For sampling of potable water including water fountains, faucets, and showerheads, two samples using a 1-liter or 1000mL sterile screw-capped plastic bottle, should be used. Collect a “pre-flush” or “first draw” sample by draining the first 1000mL of water into a bottle. A second sample, or a “post-flush” or “second draw” sample, should be taken after the water is run for approximately 60 seconds. An additional sample should be taken from faucet aerators and showerheads. Remove the aerators aseptically and take swabs of the inside of the faucet and showerheads as far as you can reach with a swab. Swirl the swab on the inside of the pipe three times. For non-potable water sampling from sources such as cooling towers, chillers, condensate pans, sprinklers, water walls, etc., a 250mL water sample should be collected from the bottom or side of the vessel or reservoir. The specimen should be concentrated by filtration, treated with an acid buffer to enhance Legionella recovery, and cultured on a selective buffered charcoal yeast extract (BCYE) agar medium. Culture essays are the most common tests used to detect Legionella in the environmental and biological samples. Rapid PCR-based methods are also available.

Control methods are designed to disinfect an entire water distribution system and include thermal super heat flush, hyperchlorination, and copper-silver ionization. Control methods designed to disinfect only a specific portion of a water distribution system include ultraviolet light sterilization, ozonation, and instantaneous steam heating. A combination of the two control methods are usually used to eradicate Legionella colonies. The EPA has established a Maximum Contaminant Level Goal (MCLG) of zero organisms for drinking water. However, a MCLG is a non-enforceable guideline based solely on an evaluation of possible health risks, taking into consideration a margin of public safety. The EPA has established the Safe Drinking Water Hotline, a toll-free number for further information on drinking water quality, treatment technologies, and for obtaining Health Advisories or other regulatory information (800-426-4791).

For further information on all your Legionella concerns, please contact McAlister GeoScience.