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EWP: How many legionellae dwell in residential buildings?

In the May issue of energy | water practice, expert magazine of the energy and water industry, first results from the status analysis of the Institute for Hygiene and Public Health of the University of Bonn (ihph) on the occurrence of Legionellae in drinking water installations were published. The great numbers of tests that were assessed lead the authors to one question: How many drinking water installations are subject to testing nationwide?

The ihph-status analysis had to deal with an enormous volume of drinking water data. 1,020,000 data sets were aggregated and assessed. It has been the wolrd’s largest research work on Legionella in domestic drinking water installations with central heating.

Elicitations were conducted with laboratories and drinking water monitoring contractors (n > 1 Million sampling results). Aims of the current project were the development of a systematic, hygienic-microbiological status analysis for the presence of Legionella in drinking water plumbing systems, explicitly including commercially used drinking water plumbing systems, the inductive and explorative examination of risk factors for Legionella and the estimation of the hazard potential.

The technical threshold level for Legionella (100 colony forming units (CFU) in 100 ml water) was exceeded in 5.6% of all samples (n=1,020,328). In 16.5% of all buildings (n=100,213) at least at one tap (sampling point) an exceedance of the technical threshold level was detected in the years 2012 to 2015. The water temperature was observed to be an important risk factor for culturally detectable Legionella (rs=-0.22; p=<0.001; n=502,009).

The article (written in German) can be downloaded here.

ewp-article Legionella in residential builidngs by Becker-Kaiser/Pikarek