Legionella control relies on regularly checking and treatment of sources that are likely to provide favourable conditions for the Legionella bacteria to breed. The most common sources for harbouring Legionella pneumophila, are cooling towers, industrial sized air-conditioning systems, domestic hot water systems, fountains, swimming pools and whirlpool spas. The Legionella bacteria are also naturally present in small quantities in rivers, streams, pools, lakes and reservoirs.
Legionnaires disease is spread when the bacteria is suspended in droplets of water and carried by the wind or through a buildings air-conditioning system. Results of tests by a legionella besmetting French team of scientists found that Legionella control that was poor could lead to the bacteria being carried up to 6Km by the wind. In 2003-2004 a case in Pas de Calais had 86 confirmed cases and 18 deaths. It was discovered that the source of the outbreak were the cooling towers of a petrochemical plant and the furthest noted cases were up to 6Km from the site.
The European Working Group for Legionella Infections (EWGLI) was set up as a response to the problem and established a set of principles and courses of action that company’s were obliged to follow in order to closely monitor potential sources of Legionella.
The EWGLI recommends that temperatures above 50 degrees Celsius will kill the majority of bacteria or leave them unlikely to multiply. Temperatures between 35 degrees Celsius and 45 degrees Celsius is where the greatest reproduction of the bacteria takes places and anything from 20 degrees Celsius to 50 degrees Celsius is when growth takes place. Any temperature below 20 degrees Celsius the Legionella bacteria can survive but will be dormant.
The most ideal forms of Legionella control are either by maintaining a temperature that is below 20 degrees Celsius and above 50 degrees Celsius, or by the use of chemical methods. Copper-silver ionisation helps to remove sludge and also removes the food source that aids bacterial multiplication. The use of chlorine dioxide is another form of Legionella control that will cut down on the problem; as does the use of ultraviolet light and ozone that will provide short-term solutions.
Chlorine treatments can eradicate the problem just as long as they are carried out every 3 – 5 weeks. Copper-silver ionisation, when used effectively, can work during the course of a week. Chlorine dioxide has a track record of successfully tackling the problem of Legionella dating back to 1945. There is little impact on it from water corrosion, pH values or inhibitors like phosphates and