Legionella prefer it warm and moist. The rod-shaped bacteria live exclusively in water, are capable of actively propelling itself along using its tail called a flagellum, and are pathogenic to humans, causing disease. Legionella pneumophila is one of the more common strains and a very important infectious agent. It causes legionellosis, popularly known as Legionnaires disease.  

The pathogen's name was coined by the American Legion, a United States Army veterans association. Back in 1976, at the association's 58th convention, twenty-nine people ended up dying in a Philadelphia hotel. It wasn't until half a year later that scientists identified Legionella pneumophila as the culprit behind the epidemic. Ever since, the bacterium carries the name of its first documented victims.  

The germs are happiest in warm, stagnant water and proliferate in the warm water tanks of radiators, air conditioners, and plumbing that is rarely used. Legionella are reliably killed off at temperatures in excess of 70 degrees C. If the water temperature inside the plumbing drops below 55 degrees C, legionella start to proliferate.

For healthy individuals, drinking legionella infested water is not a cause for concern but if the bacterium somehow manages its way into the lungs along with water vapors, as during showering or in air conditioned rooms, it can cause severe pneumonia. Whether the infested water is in fact dangerous and, if so, how dangerous depends, to a large extent, on the individual bacterial strain that is present in the water vapor. Fourteen serotypes of Legionella pneumophila alone have been identified, not all of which are pathogenic.  

Difficult proof

Legionelloses often times don't affect single individuals but large groups of people sharing public pools, hotels, air conditioned shopping malls, even hospitals. In Germany, 15 to 30 thousand new cases of legionellosis are reported annually. Between 5 and 8 percent of them end up killing the infected parties. Since legionella are found practically anywhere warm stagnant water is found, the successful identification of the source of the infection is key. Unfortunately, legionella are difficult to isolate and grow in a lab - making their study a real challenge.

HZI scientists have developed diagnostic tools on a molecular level that can be used to rapidly detect and identify legionella. Using this method, in the case of an epidemic outbreak, the more dangerous strains can be readily distinguished from those that don't pose a threat to public health, allowing scientists to quickly locate and shut down the source of the infection.  

This method, which also allows for filtering legionella from large bodies of water - like drinking water reservoirs - for their direct analysis, has made growing bacteria in the lab, which can be a real challenge, obsolete. The method is highly effective in preventing outbreaks of legionellosis in potable water systems.

(Dr Jo Schilling)

Audio Podcast

  • Legionärskrankheit – Wissenschaftler auf Spurensuche in der Wasserleitung Legionellen warten überall auf uns wo warmes Wasser gespeichert wird – in Wasserleitungen, Klimaanlagen, Schwimmbädern. Einige wenige dieser Bakterien können schon ausreichen, um bei uns eine schwere Lungenentzündung zu verursachen. Häufen sich Fälle – etwa in einem Einkaufszentrum oder einem Schwimmbad – gehen Wissenschaftler auf Legionellensuche. Manfred Höfle hat eine Technologie entwickelt, mit der er genau die Legionellen findet, die die Menschen krank machen. Begleiten Sie ihn bei seiner Detektivarbeit...

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