The Detection Limits of Legionella According to the EU Directive 2020/2184. Could That Be Too Permissive?

Introduction: The problem of detecting legionella after a case of legionellosis from the source of environmental contamination has been known since a long time ago. Legionella is a bacterium present in various natural and artificial habitats and especially in surface fresh waters. It is found in greater concentration in warm waters, at temperatures between 20 °C and 42 °C. The greatest risk factor for humans is represented by the presence of Legionella in water distribution systems in hospitals, medical equipment (e.g. respirators, dialyzers, inhalers, humidifiers, water, massage equipment used in balneotherapy) and turbines used in dental practices, especially for hospitalized individuals. In the EU directive 2020/2184, issued by the European parliament on 16/12/2020, the concentration of Legionella was added to the parameters to be determined in assessing the quality of drinking water intended for human consumption. The objectives were to improve the quality standard of drinking water, reduce the consumption of bottled water and consequently reduce plastic waste. The WHO notes that Legionella causes the greatest burden from a health point of view and it is included among the parameters that require careful monitoring with a limit of less than 1000 CFU/L. The aim of this report was to evaluate the new EU directive 2020/2184 on the light of our laboratory experience.

Materials and methods: A total of 459 samples were processed at our Hygiene of food Laboratory - Department of Medical Sciences and Public Health. All statistical analyses were conducted using the SPSS statistical package (version 23 for Windows. SPSS, Inc. Chicago, Ill).

Results and discussion: Of the 67 structures examined where the cases occurred, 35 showed samples with at least one over-threshold value considering the reference value of 100 CFU/L, whereas using the new limit of 1000 CFU/L, only 25 structures resulted as having at least one sample above the threshold. In our experience as a regional reference laboratory for Legionella research, the increase from 100 CFU/L to 1,000 CFU/L could lead to a lower alert level. In fact, in the period between October 2017 and October 2021, the median value of CFU/L in presence of a case was 0 (0-100). Despite the large amount of studies on Legionella only a few relate the withdrawals and the consequent CFU/L with the confirmed cases of legionellosis, as in our analysis. The 75° percentile values of the Legionella concentration equal to 100 CFU/L in all samples associated with cases and clusters leads us to hypothesize that the limit equal to 1000 CFU/L that will be introduced for environmental monitoring as per recent European regulations may not be sufficiently protective for minimizing risk in the population, especially in healthcare facilities where fragile patients are assisted.