Peace was broken in "Paxmontana". A year ago an American tourist was stricken with legionnaires’ disease (cf. box) after staying at a hotel in the central region of Switzerland and died later in Germany. An inquiry confirmed the suspicion that the warm water of Paxmontana contained an elevated level of the dangerous bacterium Legionella pneumophila. It remained unclear, however whether the deceased person had been infected at the hotel.

Companies want investigation

A few reports on the victims of the legionnaires' disease abroad appeared in the media, and after these initial reports the issue seemed to disappear from the agenda in Switzerland. Does this mean that legionella is no longer a topic and that we can afford to be complacent? A certain scepticism exists in some cantons concerning this bacterium, which multiplies at temperatures between 20 and 45 degrees Celsius and can cause legionnaires' disease in humans by inhalation of aerosol. Earlier this year, in spring, the “Laboratorium der Urkantone” (an intercantonal laboratory in central Switzerland) for example was asked to examine the warm water systems of 17 different enterprises. Of the 88 collected samples, 24 showed traces of legionella stemming from the enterprises. According to Dr. Beat Kollöffel of the “Laboratorium der Urkantone” suitable measures were immediately taken to eliminate the legionella. In view of these results the vociferous cry of the regional newspaper "Boten der Urschweiz" with the heading "Laboratory confirms, legionella ubiquitous" seems somewhat exaggerated.

A rise in the number of diagnosed cases

So, is everything under control? Perhaps not quite. After all, according to statistics from the Swiss Federal Office of Public Health (BAG) (2) 126 people fell ill with legionnaires' disease in 2001 and 13 of them died as a result. For 1999 the corresponding figures were merely 69 and 7, respectively. The increase probably reflects better possibilities of identifying the illness, says BAG. For the current year BAG gives the following numbers: 70 confirmed and 40 suspected cases. Will we just have to accept this? At present, no systematic strategies are in sight with which to come to grips with it. This is because, as BAG explains, no scientifically sound and objective data exists, even for threshold values, and diagnosis depends on a consensus among experts. In the February issue of its Bulletin, BAG repeats its recommendations on water temperature in plumbing installations. Hot water in a boiler should be heated to 60°C at least once a day and should be 50°C when it comes from the tap.

ETH Professor Hubert Hilbi (centre) with Dr. Jörg Mampel (left) and PhD student, André Tiaden, examining the formation of biofilm with legionella. large

Successful in practice

Naturally, Hans Gössi is fully aware of these recommendations. As owner of the company Gössi AG, Energy Systems, Küssnacht, (3) his attention has been fixed on the problems surrounding legionella for a long time. He himself developed a system for mixed water that prevents legionella contamination. This system does not rely on an increase in temperature of the grid-type network but on a lowering of temperature and the addition of ions. With the installation of a so-called Gössi-Mat the water temperature can be increased once a day up to boiler temperature in order to induce a thermal disinfection. It is also a means of saving considerably amounts of energy with its mixed water system. Lower temperatures also have the added bonus of hindering calcium deposits in pipes and tubes. This is important in so far as such deposits encourage the growth of biofilms, which can also harbour legionella. In a test, carried out by the laboratory at the University of Zurich after a renovation project where the Gössi-System was installed, no trace was found of legionella.

To be discouraged in human beings: legionella infected macrophage. The picture shows legionella expressing green fluorescent protein (GFP) (picture: Hubert Hilbi). large

Wanted: Scientific groundwork

Even though Gössi has thus succeeded in mastering legionella, he is still not fully satisfied. On the one hand, he finds the recommendation to increase the water temperature problematic with regard to the need to save energy and the danger of calcination. On the other, he would like to have conclusive and scientifically founded proof once and for all, so that this problem can be systematically addressed in Switzerland, too.

This is why he took the initiative. He contacted the microbiologist, Hubert Hilbi, ETH professor since last year and an expert on legionella (4). Their mutual interest led to a project, foreseen to run several years, which was recently granted by the Commission for Technology and Innovation (CTI). Six entities, Geberit, Victorinox, Feuron, the Water Company Küssnacht and the Swiss Federal Office of Energy are supporting the project, which was launched on the 1st of August.

Hilbi is optimistic and gratified that private companies are willing to invest in fundamental research. In a first three-year phase, research is to be carried out that delivers some answers to the question of how biofilm is formed. "Nothing is known at the molecular level on legionella biofilm," says Hilbi outlining the situation. Basically, all that is known is that bacteria generate 3-dimensional heterogeneous structures. "This is probably one of the reasons why biofilm is far more resistant to chemical and physical disinfection or antibiotics." Moreover, the formation of biofilm and virulence properties that aid infection are often regulated by the same mechanisms.

Genes for cell density

The first aspect Hilbi is turning his attention to is how the cell density of legionella affects genetic regulation. He already has a starting point here. In the genome of legionella, genes – that in other bacteria have the function of regulating cell density – were identified. PhD student, André Tiaden, will be examining what happens when these genes are extracted from legionella. It is possible that the bacterium will lose its virulence. The more difficult part, which is being carried out by Postdoc Jörg Mampel, is the attempt to reproduce legionella biofilm in the laboratory. Once these processes are better understood, Hilbi sees good chances of turning towards more application-oriented problems.

Shower generation on the move

What is Hilbi's estimation of the situation regarding the threat of legionella? For him, too, it is difficult to assess, and the need for fundamental research indisputable. Moreover, he points out that the danger arising from legionella could increase as the people now entering homes for the elderly or similar institutions belong to the generation that is used to taking showers. This means that the probability of contracting legionella via shower aerosols could rise among a group of people who are most naturally at risk.