Damian Cohall, Contributor

Legionnaire's Disease is a lung infection (pneumonia) caused by a bacterium named Legionella pneumophila. The name Legionella pneumophila was derived from the original outbreak at the 1976 American Legion Convention in Philadelphia. This disease is caused by bacteria that belong to the family Legionellaceae and this family now includes 48 species and over 70 serogroups. Approximately half of these species have been implicated in human disease. Legionella pneumophila is responsible for approximately 90 per cent of infections. These organisms are readily found in natural aquatic bodies and some species have been recovered from soil. The organisms can survive in a wide range of conditions, including temperatures of 0- 63º C, pH of 5.0-8.5, and dissolved oxygen concentrations of 0.2-15 ppm in water. Temperature is a critical determinant for Legionella sp proliferation.

The major source of the Legionella sp bacteria is water distribution systems of large buildings, including hotels and hospitals. The bacteria have been shown to attach to and colonise various materials found in water systems, including plastics, rubber and wood. Main modes for its transmission are cooling towers, mist machines, humidifiers, whirlpool spas and hot springs. Colonisation of hot water tanks is more likely when tank temperatures are between 40-50ºC (104-122º F).

There are two main ways by which persons contract Legionnaire's disease:

a) Persons contract the disease when the organism is aerosolised in water and people inhale the droplets containing Legionella.

b) Persons also contract the disease when the organism enters into their lungs by the process of aspiration. Aspiration means choking such that secretions in the mouth get past the choking reflexes and instead of going into the oesophagus and stomach, mistakenly enter the lung.

Symptoms of Legionnaire's Disease

The incubation period of Legionnaire's disease is two to 10 days. The incubation period is the time it takes before symptoms of the illness appear after being exposed to the bacteria. Persons with the disease may feel tired and weak for several days. Most persons who are admitted to the hospital develop high fever often greater than 39.5ºC (103ºF). Coughing can be the first sign of a lung infection. The cough may be sufficiently severe to cause sputum production (coughed up mucous). Gastrointestinal stomach symptoms are common with diarrhoea being the most distinctive symptom. Many patients have nausea, vomiting and stomach discomfort. Other common symptoms include headaches, muscle aches, chest pain, and shortness of breath.

Treatment

The disease is not contagious. If a patient is treated with appropriate antibiotics near the onset of pneumonia, the outcome is excellent, especially if the patient has no underlying illness that compromises his/her immune system. For patients whose immune systems are compromised, including transplant recipients, delay of appropriate therapy can result in prolonged hospitalisation, complications and death.

Many antibiotics are highly effective against Legionella bacteria. The two most potent classes of antibiotics are the macrolides (azithromycin), and the quinolones (ciprofloxacin, levofloxacin, moxifloxacin, gemifloxacin, trovofloxacin). Other agents that have been shown to be effective include tetracycline, doxycycline, minocycline and trimethoprim- sulfamethoxazole. Erythromycin, the former antibiotic of choice, has been replaced by more potent and less toxic antibiotics.