Contamination of water supply network installations
The formation of stagnant water, the presence of biological layers, sediment and corrosion products on the inner surface of pipes promotes contamination of drinking water systems with Legionella bacteria. The greatest risk of the occurrence and multiplication of these bacteria in water supply systems is associated with hot water systems. The main places where these microorganisms can be found are dead-end sections of the network, scale-covered system components, showers, faucet spouts, and strainer caps of sink faucets. Failure to maintain the temperature regime for hot water, i.e., temperatures below 50°C, creates conditions for Legionella to grow. Therefore, the quality of hot water should be subject to systematic monitoring to ensure the health safety of its users. The microbiological requirements to be met by hot water and the procedures to be followed in the event of the presence of Legionella bacteria in numbers exceeding acceptable criteria are included in the Decree of the Minister of Health of December 7, 2017, on the quality of water intended for human consumption.
Legionella can also develop in cold water systems, especially in the summer. With inadequate insulation of the network, there is an increase in the temperature of cold water resulting in a deterioration of its microbiological quality.
Infection
Infection occurs through inhalation, which is the entry into the respiratory tract of an aqueous aerosol with a droplet diameter of 0.2 to 5.0 µm containing Legionella bacteria. People with malfunctioning immune systems and comorbidities, intensive care unit patients, chemotherapy and transplant patients are particularly vulnerable. The risk of contracting legionellosis increases with age, with men over the age of 50 most commonly affected.
Not all species of Legionella bacteria cause human disease. Among the recorded cases, 80-90% are caused by Legionella pneumophila species. Legionellosis comes in two clinical varieties: with a relatively mild flu-like course and a rapidly progressive pneumonia with neurological disorders. Because Legionella pneumophila bacteria produce β-lactamases and multiply inside macrophages (immune cells), penicillin treatment, which is used in typical pneumonia, is not effective. Therefore, macrolide antibiotics such as erythromycin are used in
the treatment of legionellosis. The mortality rate of patients with the pulmonary form of legionellosis is relatively high (15-20%), and it depends on the health status of the affected individuals and the virulent properties of the bacteria, that is, their ability to cause the disease.
No human-to-human transmission was found. Drinking water contaminated with these bacteria does not lead to infection. The risk exists only if the fluid is choked and enters the respiratory tract.
Bacteria of the genus Legionella
Legionella bacteria are motile bacilli whose natural habitat is inland water, sea water and soil. The optimal temperature for their growth is between 20°C and 45°C. If they reside in protozoan cells, they can multiply even at 67°C. They show great adaptability to different environmental conditions and have been isolated from water temperatures ranging from 0°C to 70°C. Legionella bacteria usually occur with other microorganisms - heterotrophic bacteria, protozoa, fungi and algae to form biofilms that are difficult to remove.
Devices requiring constant supervision
The source of Legionella infection is most often equipment and systems that produce water-air aerosols, such as:
- showers,
- air-conditioning systems with water fan coolers,
- respirators,
- humidifiers.
- Aerosol-generating devices that can be a factor in collective illness include therapeutic and whirlpool baths (whirlpools).
Elevated water temperature and failure to ensure proper sanitation of equipment, promotes the growth of Legionella bacteria and creates an increased risk of infection. Therefore, the concentration of free chlorine in whirlpools should be higher than in regular swimming pools.
In addition, whirlpools should always be drained, washed and disinfected after each day of use.
Preventive measures
In order to prevent infections caused by Legionella bacilli, it is necessary to limit the use of equipment and systems that produce water aerosol such as municipal fountains, water curtains, maintain a sanitary regime of humidifiers and inhalers, carry out systematic washing and disinfection of water system components: water taps and shower heads, as well as air conditioning equipment.