Legionella are rod-shaped bacteria that are found in low concentrations in drinking water. In small quantities, they pose no risk to humans – but if their concentration rises sharply, Legionella can cause the dangerous Legionnaires’ disease. Infection occurs by inhaling tiny droplets of water, for example when showering or bathing in a whirlpool. We give tips on which symptoms you can recognize an infection with Legionella and inform you about the regulations for testing drinking water.
Legionella in drinking water
Legionella bacteria occur naturally in soil and surface water. In small numbers, the bacteria are also present in groundwater. Therefore, smaller amounts of Legionella may also be present in our drinking water. In cold drinking water the concentration is usually very low, because the bacteria multiply very slowly at temperatures below 20 degrees. Between 30 and 50 degrees the multiplication proceeds optimally, a safe killing of the bacteria takes place starting from approximately 60 degrees. Legionella usually multiply in drinking water when water systems are operated incorrectly or the water is not heated sufficiently. Therefore, the temperature in the central hot water tank should be at least 60 degrees. This reduces the risk that legionella can survive and multiply.
Infection during showering
Legionella in drinking water is not a problem when drinking, cooking or washing, here there is usually no risk of infection. In fact, infection can only occur through inhalation of minute water droplets – so-called aerosols. This can happen, for example, when showering. In addition, however, infection can also occur in swimming pools – for example, by bathing in whirlpools, waterfalls or through contact with other water sprays – as well as through air conditioning systems.
Infection with legionella
There are two different courses of infection with Legionella – Legionnaires’ disease and Pontiac fever. In both forms, symptoms such as the following may occur:
- Malaise
- Headache
- Fever and aching limbs
- Cough and chest pain
- Diarrhea
- Confusion
The elderly, people with a weakened immune system and smokers are at particularly high risk of infection. Men are also significantly more likely to be affected by Legionella infections than women.
Legionnaires’ disease and Pontiac fever.
Legionnaires’ disease is a severe form of pneumonia. The incubation period is usually between two and ten days, but in extreme cases it can be as long as two weeks. If Legionnaires’ disease is not treated, it takes a fatal course in around 20 percent of cases. Generally, the disease can be treated well by administering antibiotics. Pontiac fever occurs much more frequently than Legionnaires’ disease – in Germany there are around 100,000 cases per year. In contrast to Legionnaires’ disease, the incubation period is much shorter, usually only up to two days. Pontiac fever is a flu-like illness that runs with fever, but usually without lung involvement. Usually, the infection heals on its own after a few days.
Legionella testing is mandatory
New regulations in the German Drinking Water Ordinance of November 1, 2011, require owners of drinking water installations to have their drinking water tested for legionella at regular intervals. One- and two-family houses are exempt from the testing obligation. If there is an infestation with legionella, it is important to find and eliminate the source. In addition, it is also important to determine the cause of the infestation – for example, a dead water pipe in which the water has been standing for a long period of time. Options for remedying the infestation include heating all water to above 70 degrees and chemical disinfection with chlorine.
Legionella: Limits
When testing drinking water for Legionella, certain limit values must be observed. A value of less than 100 CFU/100 milliliter (CFU = colony-forming unit) is considered acceptable. If values are between 100 and 1,000 CFU, remediation must take place within one year. If values above 1,000 CFU are measured, remediation measures must be initiated in the short term.From 10,000 CFU, a danger level is reached that entails immediate measures such as a shower ban. In high-risk areas, the Legionella value must be 0 CFU. High-risk areas include, for example, intensive care units, neonatal intensive care units and transplant units. Drinking water must also be free of Legionella in wards that treat patients with compromised immune systems, such as oncology.
