The species Legionella pneumophila is divided into sixteen subgroups (called serogroups).

Legionnaires’ disease is a potentially fatal illness involving pneumonia.  Early symptoms include musclepain, loss of appetite, headache, high fever, dry cough, chills, confusion, disorientation, nausea, diarrhea, and vomiting.  Later symptoms include chest pain and difficulty breathing.  It is difficult to distinguish this disease from other pneumonias. Early diagnosis and treatment are extremely important.  Treatment consists of intravenous administration of antibiotics.

There are no reports of naturally infected animals.  Scientists may artificially infect experimental animals (such as guinea pigs and gerbils) with Legionella to study disease.

Legionella are mostcommonly found in water, including groundwater, fresh and marine surface waters, and potable (treated) water.  Legionella are protected againist standard water disinfection techniques, by their symbiotic relations with later microorganisms.

Legionella are relatively resistant to standard water disinfection procedures and, can occur in potable water. These bacteria have been found in water distribution systems of hospitals, hotels, clubs, public buildings, homes, and factories.  Other waters in which Legionella have been found include cooling towers, evaporative condensers and whirlpools.  These bacteria may be transported from potable water to air by faucets, showerheads, cooling towers, and nebulizers.

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.  Humans may inhale contaminated aerosols or aspirate small amounts of contaminated drinking water. No vaccine is available to prevent infection.

Cases of legionellosis (any disease caused by Legionella) have been reported in North and South America, Asia, Australia, New Zealand, Europe, and Africa.  National surveillance programs areconducted in the United States, 24 European countries (including England), Australia, and New Zealand.  Legionellosis outbreaks most frequently have been attributed to contaminated potable water, cooling towers, or components of water distribution systems.  Outbreaks in hospitals have been linked to hospital potable water supplies, air conditioning systems, and cooling towers.  Travelers can be exposed to Legionella in contaminated hotel potable water or contaminated whirlpool spas. Community outbreaks are caused by exposure to a wide variety of sources, but potable water and cooling towers are the most common.

Environmental samples should be collected by swabbing areas where water flows (such as faucets and shower heads).  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 assays are the most common tests used to detect Legionella in environmental and biological samples.

Selecting one or a combination of these two types of control methods would be best for eradicating Legionella colonies and preventing recolonization of the water distribution system.