What is legionella and Legionnaires' disease?

Legionnaires’ disease is a lung infection caused by bacteria called Legionella pneumophila. Legionnaires’ disease caused by these bacteria has two forms: pneumonia with severe symptoms and Pontiac fever, which is a milder type.

legionella ozone disinfection

Why is it called Legionnaires disease?

Legionnaires’ disease got its name from an epidemic that occurred after a celebratory meeting among former legionnaires in Philadelphia in the USA in 1976. It is stated that between 8,000 and 18,000 cases of legionnaires are seen in the USA every year. On average, there are approximately 200-250 reported confirmed cases of Legionnaires’ disease each year in England and Wales and it is thought that the total number of cases may be underestimated. About half of the cases are associated with travel abroad. Legionnaires’ disease, which can be seen all year round, can usually be seen in summer and early autumn epidemics. 5-15% of people who get this disease, which can be seen worldwide, die.

What are the symptoms?

Symptoms of Legionnaires’ disease appear between 2 and 10 days after ingestion of the bacteria. The patient complains of weakness and fatigue for a few days. Fever rises (>38.5°C) in most patients. Gradually, symptoms of lower respiratory tract infection develop. Cough, chest pain and shortness of breath occur. Patients often cannot produce sputum. Nausea, vomiting, abdominal discomfort and diarrhoea may occur. Other common symptoms are headache and muscle pain; In some cases, nervous system findings that can progress to restlessness, distraction, distress, confusion and coma can be observed.

Laboratory tests have shown patients that the kidneys are not functioning properly. A chest X-ray usually shows the result as pneumonia. Legionnaires’ disease is difficult to distinguish from pneumonia just by looking at the symptoms. Other tests are required for diagnosis.

Patients with Pontiac fever have complaints of fever and muscle pain. The disease usually did not turn into pneumonia. They can stand up without treatment in two to five days. The time between being affected by Pontiac fever and showing the symptoms of the disease is shorter; varies from a few hours to 2 days.

Who is at risk?

Legionella bacteria have a very weak potential to cause infection. Only 1-5% of individuals exposed to the bacteria may develop the disease. For the disease to occur in the individual, there must be a predisposition. In healthy individuals with a normal immune system, infection often does not develop, even if the agent is ingested. For the disease to occur, the individual must have certain risk factors. The most important risk factors are the effects that weaken the person’s airway resistance or general body resistance. These are in summary:

• people over 45 years of age
• smokers and heavy drinkers
• people suffering from chronic respiratory or kidney disease
• diabetes, lung and heart disease
• anyone with an impaired immune system

How do people get Legionnaires disease?

People contract  Legionnaires’ disease by inhaling small droplets of water (aerosols), suspended in the air, containing the bacteria. Certain conditions increase the risk from legionella if:

  • the water temperature in all or some parts of the system may be between 20-45 °C, which is suitable for growth
  • it is possible for breathable water droplets to be created and dispersed eg aerosol created by a cooling tower, or water outlets
  • water is stored and/or re-circulated
  • there are deposits that can support bacterial growth providing a source of nutrients for the organism eg rust, sludge, scale, organic matter and biofilms

Cases of Legionnaires’ disease are often the result of infections caught in the UK, but a number of cases occur abroad. Useful advice on travel can be found from the European Working Group for Legionella Infections (PDF(EWGLI).


  • To prevent Legionnaires’ Disease in humans by preventing the growth of Legionella Bacteria in water cooling towers, it is recommended to pay attention to the periodic maintenance of water cooling towers on the one hand and to be cautious about the problem by making “total bacteria” counts at the laboratories of the nearest health institutions at periodic intervals. This recommendation is a legal requirement in some Western Countries, and operators who do not comply with this requirement are put into legal practice by the state’s authorized public health authorities. We hope that this article will reach the law-making authorities, and a regulation to protect our citizens will be prepared and put into practice shortly regarding this issue, for which legal measures have not been taken in our country until now.

Since the subject is HUMAN HEALTH, we find it useful to expand the above-mentioned precautions paragraph as follows.

Coolant must be constantly conditioned. Continuous and controlled water conditioning eliminates the problem of “Bacteria Nest” formation. Here are the methods to prevent the formation of solid impurities, which we will describe as “Bacteria Nest”:

A. Cooling water must be filtered continuously. Since hundreds of thousands of cubic meters of ambient air passing through the tower every day, the pollution left by this air in the cooling water can only be removed by filtering the cooling water. In today’s filter technique, the most suitable filter for cooling water is the fully automatic backwash DISC filter.

B. The cooling water must be constantly chemically and physically conditioned against limestone harbouring bacteria.

  • Undesirable limestone can be prevented by keeping the feed water quality of the cooling system under control: Depending on the quality of the raw water, the feed water can be prepared by techniques such as classical softening, deionization and reverse osmosis.
  • Calcification in the cooling water system can be prevented by the chemical conditioning method.
  • Organizations that do not find the chemical method ENVIRONMENTAL can prevent the formation of calcification and algae in the cooling tower without using any chemicals, with the Ozone Generator.


C. The conductivity of the cooling water is constantly kept under control, and when the conductivity rises, some water is automatically discharged, freshwater is automatically replaced by the discharged water, and the conductivity of the cooling water is kept at a normal level.

  • The Microbiological condition of the Cooling Water is checked frequently. Once a month, a “total bacterial count” and the amount of “live” in the cooling water is observed. If the amount of Bacteria in the unit water is high, the cooling system is disinfected immediately and the above-mentioned bacteria nests are destroyed. Disinfection of Cooling Waters is generally done with chlorine types and also with chemicals called “Biocide”. In the examinations, it was seen that Chlorine did not affect the Legionella bacteria. For this reason, we should never rely on conventional Chlorine disinfection. Since 1990, the technique of conditioning the cooling water with OZONE Gas has been greatly improved. Ozone gas destroys Legionella and other bacteria and algae species. While most of the chlorine and biocides are effective at certain pH levels, Ozone Gas acts as a disinfectant at every pH level.
  • Water cooling towers should be checked periodically “monthly”. In this control, contaminants that harbour the growth of Legionella bacteria such as limestone, sediment, “biofilm” in the tower and the cooling water system should be detected and destroyed.
  • Shock Disinfection. Considering the climatic conditions of the region, it is recommended to perform shock disinfection after the complete maintenance of the tower every few months.

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