More and more often we hear about the danger of Legionella, a severe form of pneumonia caused by the Legionella pneumophila bacteria, with a mortality rate of 10-15%. But let’s try to clarify the conditions that lead to the proliferation of this bacterium and the relative treatments to combat it.

Legionella bacteria are present in both natural and artificial aquatic environments: they are found in springs, including thermal springs, in rivers, lakes, vapors and soils. From these natural environments it reaches the artificial ones such as the city ducts and the waterworks of the buildings, e.g. reservoirs, pipes, fountains and swimming pools. The bacterium is transmitted by inhalation of infected water droplets, i.e. contaminated aerosols. All places where contact with nebulized water is possible are possible sources of contamination.

The most favorable conditions for the proliferation of the bacteria are:

  • stagnation of water and presence of oxygen;
  • water nebulization with formation of microdroplets with diameters ranging from 1 to 5 microns;
  • presence of encrustations and sediments;
  • presence of nutritive elements: biofilm, slag, iron, limestone ions and other microorganisms;
  • temperature between 25 and 42 ° C (the growth of bacteria is maximum at about 37 °).

Legionella infections are linked to the pollution of water supply systems. In old systems without suitable treatment equipment, limestone crusts and corrosive substances form an ideal shelter for legionella colonies. The poor cleaning of the plants, the lack of periodic sanitizing interventions, the use of tanks without bottom bleeding, determine the formation of the biofilm, that turbid material, mainly consisting of sugars, that is often found in tubes and tanks and represents a source of nourishment for Legionella.

Here is a list of plants and related ‘critical’ points at greatest risk:

  • Cooling towers (open circuit wet towers, closed circuit towers, evaporative condensers);
  • Conditioning systems (wet pack humidifiers, spray air washers, nebulizers, drop separators, filters, silencers);
  • Sanitary systems (pipes, especially if obsolete and with inside deposits, closed pipe sections, storage tanks, valves and faucets, shower heads);
  • Emergency systems (decontamination showers, eye wash stations, sprinkler systems);
  • Swimming pools and whirlpools;
  • Decorative fountains;
  • Oxygen delivery apparatus;
  • Cooling systems.

The strategies to combat the proliferation of legionella lie in prevention and in a professional management and maintenance. The treatments against the causes, i.e. the biofilm and the encrustations, once the proliferation has been verified, are to be evaluated case by case.

Below we list the most common:

  • Heat treatment, in which the water is kept at a temperature above 60 ° C, a condition in which Legionella is inactive;
  • Continuous chlorination: generally, the sanitation of the circuit takes place within 30 days, with a dosage below the maximum concentration limits imposed by law;
  • Shock chlorination: the sanitization times of the entire water circuit are much reduced compared to the previous mode. However, this treatment involves the suspension of activities related to the use of water since the dosage of sanitizing products is higher than the maximum concentration limits set by law;
  • Chemical disinfection, which allows continuous disinfection while maintaining the characteristics of water potability; the molecules of the bactericidal chemical can enter the biofilms (natural habitat of Legionella), constituting a very prolonged action over time;
  • Ultraviolet rays, able to inactivate the bacteria that pass through the ray emission equipment;
  • Terminal filters: directly applied to the sampling point, they form a mechanical barrier (0.2 μm) to the bacterium but must be replaced with a certain periodicity. They are usually applied in combination with chlorine dioxide, in very high-risk areas (showers for large burns, neonatology showers, etc.).

From a regulatory point of view, there are various initiatives designed to monitor legionellosis. Managers of accommodation facilities, collective facilities (sports and recreational facilities, fairs, wellness centres, etc.) and of health and spa facilities (hospitals, nursing homes, etc.) are obliged to carry out a Biological Risk Assessment and a Self-control Plan and Risk Management specific to the structure developed.

Find out more about sanitary water and collective use technologies. Technoacque experts will be happy to provide you with any kind of information on bactericidal products and water treatment plants, do not hesitate to contact us.

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