The Association of German Engineers (VDI) extended its guidelines to include rapid testing of Legionella in cooling towers in the VDI guideline 4250-2.

As in many countries around the world, the risk posed by Legionella, the water-borne bacteria behind a serious lung infection known Legionnaires disease, became very real in 2013. That year, a Legionnaires disease outbreak in the German town of Warstein led to 159 suspected cases of the dangerous infection. The count included 78 cases that were laboratory confirmed, including one known fatality. The following year, Legionella was also found in a cooling plant in Jülich, Germany. The plant was immediately shut down and disinfection measures had to be put in place. [1] [2]

It's no secret that the outbreak caught the attention of the Association of German Engineers (also called the Verein Deutscher Ingenieure or VDI), which had long worked to establish guidelines around the testing and prevention of Legionella, particularly in industrial cooling towers and other facilities with water systems. Since then, the question facing this professional organization of about 135,000 engineers and natural scientists: How do you quickly and accurately identify Legionella, as every moment matters when it comes to an outbreak such as what occurred in 2013 and 2014?

Updated VDI Guidelines Now Include Flow Cytometry

Recently, we’re pleased to report that VDI is officially updating its guidelines to allow for rapid testing of Legionella using flow cytometry and specific cell separation which is used by the rqmicro.COUNT instrument. Operators of cooling towers and laboratories in Germany are now able to use rqmicro.COUNT to detect Legionella contamination in the event of an outbreak or as part of the VDI guideline 4250-2. This approval is the result of the successful independent validation performed over the course of the last 2 years. 

 Watch a recorded version of the webinar: Expert Laboratory Legionella – Rapid quantification and subtyping of L. pneumophila in evaporative cooling systems

Understanding Flow Cytometry

Why would VDI even consider changing testing methods to detect bacteria in the first place? 

After all, traditional methods based on cell culturing – that is, growing suspected bacteria on petri dishes – have been used for years. The answer is that flow cytometry—an optical measurement technology which can analyze single cells at a very high speed — has proven to be superior over cell culturing in several ways: 

  • Rapid Results: Flow cytometry provides much faster results compared to culturing methods because simply, it does not require cell culturing. Culturing methods typically require incubation for at least 24 hours to allow bacterial growth. Flow cytometry, on the other hand, is able to detect single cells and hence is not dependent on the highly variable and slow process of cell culturing.
  • Quantitative Analysis: Flow cytometry provides quantitative data by directly counting bacterial cells. It can also provide information about cell size and cell viability. Culturing methods, on the other hand, generally provide qualitative results, indicating only the presence or absence of bacterial cells or broadly estimate the number of cells based on the colony forming units (CFU).
  • Detection of Viable and Non-Viable Cells: Flow cytometry can distinguish between viable and non-viable bacterial cells by utilizing different types of markers. Culturing methods generally detect a sub-group of viable cells which has grown on the culture media.
  • High Sensitivity: Flow cytometry can detect low concentrations of bacteria due to its sensitivity and independence from cell culturing. It can provide sensitive detection even in samples with low bacterial counts or in presence of biocides or in treated water samples, which may be challenging with culturing methods.
  • Automation and Standardization: Flow cytometry allows for automated sample processing and data analysis, reducing the potential for human error and increasing standardization. Culturing methods often involve manual steps and subjective interpretation, which introduces additional variability.

Why use rqmicro.COUNT? We designed it as a portable and easy-to-use flow cytometer. It is a plug-and-play system due to the measurement on single-use cartridges and a fully automated analysis with preprogrammed gate settings. Among the benefits of the rqmicro.COUNT instrument:


First results are available after 30 minutes from taking the sample


High sensitivity on a single-cell level


Test kits available for unspecific cell counting (ICC and TCC) and specific pathogens (E. coli, Legionella) on the same platform


Connect to secure cloud platform which enables online data analysis, automated alarms and sharing of reports


Ready-to-use reagent tubes and single-use cartridges make flow cytometry easy and convenient as never before

Contact us today for a demonstration


[1] A. Maisa, A. Brockmann, F. Renken, C. Lück, S. Pleischl, M. Exner, I. Daniels-Haardt, A. Jurke. Epidemiological investigation and case-control study: a Legionnaires' disease outbreak associated with cooling towers in Warstein, Germany, August-September 2013.

[2] Jülich Forchungszentrum. Press release, 2014.: Legionella Found in Cooling Plant: Forschungszentrum Jülich Takes Emergency Measures.

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