Legionellosis is an infection caused by bacteria Legionella, notably Legionella pneumophila, and some 46 species and 70 serogroups have so far been identified. Legionella pneumophila is an aquatic organism thriving in a warm environments (25 to 45 °C with an optimum around 35 °C) and causes over 90 % of Legionnaires Disease.

‘Legionnaires’ disease is the name given to the more severe form of infection which includes pneumonia. The disease acquired its name in 1976 when an outbreak of pneumonia occurred among people attending a convention of the American Legion in Philadelphia. On January 18, 1977 scientists identified the causative agent as a previously unknown bacterium, subsequently named Legionella. An estimated 8,000 to 18,000 people get Legionnaires’ disease in the United States each year. Some people can be infected with the Legionella bacterium and have mild symptoms or no illness at all. The disease usually occurs as a single, isolated case, but outbreaks do sometimes occur, generally in the summer and early fall. Legionnaires’ disease is fatal for about 5% to 30% of individuals.

Patients with Legionnaires’ disease usually have fever, chills, and a cough, which may be dry or may produce sputum. Some patients also have muscle aches, headache, tiredness, loss of appetite, and, occasionally, diarrhea. Laboratory tests may show that patients’ kidneys are not functioning properly. Chest X-rays often show pneumonia. It is difficult to distinguish Legionnaires’ disease from other types of pneumonia by symptoms or radiologic findings alone; other tests are required for diagnosis.

The incubation period for Legionnaires’ disease is 2 to 10 days.

Legionella. pneumophila is primarily considered as a pathogen of the respiratory tract, a cause of atypical pneumonia, also known as Legionnaires’ disease. Other infections have also been reported, including haemodialysis fistulae, pericarditis and wound and skin infections. Bacteraemia is often associated with Legionnaires’ disease.

Intestinal Infection generally only occurs as part of respiratory infections.

One species, Legionella longbeachae, is contracted via the inhalation of infected compost or soil.

The most useful tests detect the bacteria in sputum, find Legionella antigens in urine samples, or compare antibody levels to Legionella in two blood samples obtained 3 to 6 weeks apart. The urine antigen test is simple, quick, and very reliable; however it will only detect legionella pneumophila serogroup 1. Also the urine antigen test will not identify the specific subtyping so it cannot be used to match the patient with the environmental source of infection.

Who contracts legionellosis?
People of any age may get Legionnaires’ disease, but the illness most often affects middle-aged and older people, particularly those who smoke or have chronic lung disease. Immunocompromised patients are also at elevated risk.

The main treatment is with various antibiotics.

How is legionellosis spread?
Legionellosis infection occurs after persons have breathed mists that come from a water source, such air conditioning cooling towers, whirlpool spas, showers etc, which are contaminated with Legionella bacteria. Persons may be exposed to these mists in hotels, workplaces, hospitals, or public places. Legionellosis is not passed from person to person, and there is no evidence of persons becoming infected from car air conditioners or household window air-conditioning units.

Legionella longbeachae, one species in the Legionella family, is found in soils and compost. Persons inhaling soil or compost dust containing Legionella longbeachae risk contracting the disease, one such sourcebeing pre-packaged bags of soil, compost, or potting mix.

Source of Legionella bacterium
Legionella organisms can be found in many types of water systems. The bacteria will grow in water temperatures from 20°C to 50°C). However, the bacteria reproduce at the greatest rate in warm, 32 – 40 °C, stagnant water, such as in certain plumbing systems and hot water tanks, cooling towers and evaporative condensers of large air-conditioning systems, whirlpool spas and ornamental fountains.

Improved design, operation, maintenance and implementation of risk management strategies for cooling towers, potable water systems and other aerosolizing equipment are the best way to limit the growth and spread of Legionella organisms.

* Below 68 °F: Legionellae can survive but are dormant
* 68 to 122 °F (20 to 50°C): Legionellae growth range
* 95 to 115 °F (35 to 46°C): Ideal growth range
* Above 122 °F (50 °C): They can survive but do not multiply
* At 131 °F (55 °C): Legionellae die within 5 to 6 hours
* At 140 °F (60 °C): Legionellae die within 32 minutes
* At 151 °F (66 °C): Legionellae die within 2 minutes
* 158 to 176 °F (70 to 80 °C): Disinfection range

The world’s largest outbreak of Legionnares’ disease happened in July 2001 in Murcia, where more than 800 suspected cases were recorded. There were 6 deaths.

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