Legionella causes legionellosis

Proven content

The main problem with Legionella bacteria results from their common colonization of both cold and hot water supply systems, bathing devices, air conditioners, etc. Legionella can become an etiological factor of severe pneumonia.

In 1976, during the Convention of the American Legion in Philadelphia, cases of severe pneumonia were reported among participants, which for most patients ended in death. The causative agent was not found during the epidemiological investigation, it was only in 1977 that it was established that the etiological factor of severe pneumonia was gram-negative bacteria of the genus Legionella. Until then, these bacteria were believed to be non-pathogenic for humans.

Mysterious water disease

Among the legionella bacteria, it is the basic species pathogenic for humans Legionella pneumophila. These bacteria are characterized by the ability to penetrate and multiply in cells, e.g. macrophages or monocytes, which allows them to avoid the activity of our immune system. An additional, very unfavorable feature for us is the ability of bacteria to produce enzymes that break down antibiotics, e.g. penicillins and their derivatives.

In natural conditions, these bacteria live in the aquatic environment. The presence of bacteria is favored by the presence of protozoa, e.g. amoebas or ciliates, in which they multiply and may remain dormant for many years in the spore forms of protozoa.

The basic problem with Legionella bacteria is that they often inhabit both cold and hot water supply systems, as well as bathing devices, air conditioners, etc. These bacteria, in particular, inhabit water devices containing sediment and rust.

Infection occurs as a result of inhaling an aerosol or choking on contaminated water. It is very important that the infection occurs through the respiratory tract (inhalation), consumption of contaminated water does not cause disease. It should be emphasized that situations that favor the formation of fine water dust (aerosols), e.g. by showers, fountains or air conditioning, are particularly dangerous. Bacteria suspended in wind-blown aerosols remain contagious up to 1 km from the source of infection.

Fortunately, no transmission of infection from one person to another is observed, so the patient does not pose a threat to the environment.

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Legionellosis = Legionnaires’ disease

It is an infectious disease that occurs all over the world. The risk of developing the disease increases with age, and the most common diseases are men aged 40-65, professionally active and traveling, tourists exposed to moisturizing devices in means of transport or hotels.

Factors increasing the incidence include: decreased immunity as a result of diseases (e.g. cancer, HIV) or immunosuppressive treatment, alcoholism, smoking, working or living in a dusty environment, long journeys – especially to tropical countries.

Legionella pneumophila infection can be as follows:

1. pulmonary form – a typical picture of legionellosis, presenting as severe pneumonia. The characteristic symptoms are: fever up to 39C, dry cough, shortness of breath, abdominal pain, vomiting and diarrhea, and disturbed consciousness. In the course of the disease, complications such as respiratory failure or renal failure may occur. Approx. 20% of patients die of legionellosis.
2. extrapulmonary form – can run as:
3. Pontiac fever – a mild flu-like illness with symptoms of fever, headaches, muscle aches, and symptoms of upper respiratory tract infection. Recovery occurs spontaneously after a few days.
4. systemic infection with symptoms of sepsis; burdened with a very high mortality rate. This form of infection is mainly observed in immunosuppressed people, e.g. after transplantation.

The diagnosis of the disease is difficult because these bacteria have specific growth requirements and not all microbiological laboratories conduct diagnostics in this direction. If a disease is suspected, the material for microbiological tests is material taken from the lower respiratory tract using a bronchoscope.

In most cases, the diagnosis of the disease is based on the results of serological tests, i.e. the detection of bacterial antigens in the urine or respiratory secretions, or determination of the titre of antibodies specific to Legionella bacteria in two blood samples.

The treatment of legionellosis involves the use of antibiotics, especially from the group of macrolides, for a period of approx. 3 weeks.

Due to the big problem that legionellosis epidemics may pose in hospitals, hotels or other public places, rules and procedures for the prevention and control of this disease have been introduced. In Poland, these rules are regulated by the Act on Diseases and Infections and the guidelines of the State Sanitary Inspection.

The basic methods of preventing and combating legionellosis are:

1. cleaning of sediment from water network tanks at least twice a year
2. maintaining the right temperature at the tips: for cold water below 20⁰C; for hot water at least 55⁰C
3. periodic water testing for the presence of bacteria – in the laboratories of Sanitary and Epidemiological Stations – the detection of more than 1000 bacterial cells in 100 ml is an indication for urgent implementation of interventions
4. lowering the air humidity
5. chlorination of water to an appropriate concentration
6. humidifying devices should be regularly cleaned of sediment and filled only with sterile water (e.g. boiled)

Research is currently underway to develop a vaccine against legionellosis.

Text: Mirosław Jawień, MD, PhD

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