Protection against Legionella

In the future, people returning to Germany after an exotic foreign holiday will see something taken for granted in a new light: When they turn on a tap at home, what comes out will be drinking water. It will be safe to drink and smell fresh instead of like the chlorine that is used in some countries to combat harmful bacteria. Hot water for the bath or the shower will also be of the same potable quality.

Until now, there has been a gap in the safeguards between the connection to the water mains and the faucet. That’s because as soon as the cold water — at about eight degrees Celsius — flows into the house piping, the water utility no longer has any control over its quality. One bacterium in particular is a source of worry here: Legionella pneumophila.

It causes a non-specific syndrome which physicians refer to as “Legionnaires' disease,” because it was first described after an outbreak affected delegates attending a convention of the American Legion in 1976. The victims had inhaled the rod-shaped bacteria while showering. Legionella infections can lead to pneumonia and kidney failure, especially in weakened or older persons. A total of 5,518 cases were recorded in Europe in 2009, with a high mortality rate of between ten and 20 percent, and the number of unrecorded cases is presumed to be high.

The bacteria are choosy. They do not multiply at temperatures below +20 degrees Celsius, and they die off within minutes when it gets hotter than +60 degrees Celsius. That means they are at home in pipes and boilers containing warm water within this temperature range. The bacteria thrive optimally at 36 degrees Celsius. They settle in the “biofilms” that inevitably form in pipe systems, shower heads, and water taps. Traditional hygiene measures scarcely affect them.

Although the skilled trades had developed mandatory rules for reducing the danger of Legionnaires' disease, legislators wanted to go further. That’s why a limit of 100 colony-forming units of Legionella per 100 milliliters of drinking water came into force as an extension of the EU drinking water directive on November 1, 2011. Systems above a certain size (see adjacent box) will have to be checked every year to ensure that they conform to the new limit.

That means an accredited sample taker will first draw 250 milliliters of water from the sampling point and fill it into a sterilized plastic sample bottle. In order to ensure that the sample only contains water from the boiler, the sampling point will first be disinfected using a 70 percent solution of ethanol. After the disinfectant has been given time to work, the boiler will be set to its maximum temperature, the water will be allowed to run for a few minutes, and the sample will then be taken.

The water sample will be sent to an accredited testing laboratory, for example to Dr. Graner & Partner GmbH in Munich. “We start the analysis within 12 hours of the sample being taken,” says Manfred Holz, who holds a doctorate in chemistry and is the Managing Director of this renowned laboratory for analytical and pharmaceutical chemistry. Here the samples end up on the lab bench, where Ralph Elbert carries out the analyses.

Elbert, a chemical laboratory assistant, explains, “We carry out the examination by observing bacterial growth on a nutrient base.” It’s a threefold test. First of all, Elbert pipettes two aliquots, each consisting of 500 microliters of the sample, onto the agar surfaces of two Petri dishes and “streaks” these drops using a Drigalski spatula. He keeps the spatula in technical ethanol, flames it, and lets it cool briefly before using it, so that the heat doesn’t kill any of the bacteria that may be present in the sample. These two dishes contain the “native,” i.e. untreated, samples.