What are Legionella?

Legionella are rod-shaped bacteria that occur in low concentrations in drinking water. In small quantities, they pose no risk to humans - but if their concentration increases sharply, legionella can cause dangerous Legionnaires' disease. An infection takes place by the inhalation of the smallest water droplets, for example when showering or while bathing in the whirlpool. We provide tips on the symptoms of Legionella infection and on the regulations for testing drinking water.

Legionella in drinking water

Legionella occur naturally in the soil and in surface waters. In small numbers, the bacteria are also contained in the groundwater. Therefore, smaller quantities of Legionella can also be found in our drinking water. In cold drinking water, the concentration is usually very low, because the bacteria multiply only very slowly at temperatures of below 20 degrees. Between 30 and 50 degrees, the propagation is optimal, a safe killing of bacteria takes place from about 60 degrees.

Legionella usually multiply in drinking water when water systems are operated incorrectly or the water is not heated sufficiently. In the central hot water tank, the temperature should therefore be at least 60 degrees. This reduces the risk that legionella can survive and multiply.

Contagion while showering

Legionella in drinking water is not a problem when drinking, cooking or washing, there is usually no risk of infection here. A contagion can namely only by inhaling the smallest water droplets - so-called aerosols - take place. This can happen, for example, while showering. In addition, infection can also take place in the swimming pool - for example by bathing in whirlpools, waterfalls or through contact with other water sprays - as well as air conditioning systems.

Infection with legionella

Legionella infection distinguishes two different types of disease - Legionnaires' disease and Pontiac fever. Both forms can cause symptoms such as the following:

  • malaise
  • a headache
  • Fever and body aches
  • Cough and chest pain
  • diarrhea
  • confusion

A particularly high risk of infection are older people, people with a weakened immune system and smokers. Men are also significantly more affected by Legionella infections than women.

Legionnaire's disease and Pontiac fever

Legionnaire's disease is a severe form of pneumonia. The incubation period is usually between two and ten days, in extreme cases, it can also be up to two weeks. If the Legionnaire's disease is not treated, it takes a fatal course in about 20 percent of cases. In general, the disease can be treated well by the administration of antibiotics.

Significantly more often than the Legionnaire's disease, the Pontiac fever occurs - in Germany, there are about 100, 000 cases per year. In contrast to Legionnaire's disease, the incubation period is significantly shorter, usually only up to two days. The Pontiac fever is a flu-like illness that occurs with fever, but usually without involvement of the lungs. Normally, the infection heals itself after a few days.

Legionella examination is mandatory

The new regulation of the Drinking Water Ordinance of 1 November 2011 obliges owners of drinking water installations to have their drinking water checked for Legionella at regular intervals. One- and two-family houses are exempted from the obligation to examine.

If an infection with Legionella is present, it is important to find and eliminate the stove. In addition, it is also important to determine the cause of the infestation - such as a dead water pipe, in which the water is over a long period of time. To remedy the infestation, among other things, the heating of the entire water to over 70 degrees and a chemical disinfection with chlorine in question.

Legionella: limits

When testing drinking water for Legionella, certain limits must be met. Acceptable is a value of less than 100 cfu / 100 milliliters (KBE = colony forming unit). For values ​​between 100 and 1, 000 CFUs, remediation must take place within one year. If values ​​above 1, 000 CFU are measured, remedial measures must be initiated at short notice. From 10, 000 KBE onwards, a danger level has been reached which will lead to 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 transplantation units. Even at wards where patients with a compromised immune system are treated, such as oncology, the drinking water must be free of Legionella.

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