Aerosols containing Legionella : an approach to metrology and detection aspects

International audienceThe bacterial proliferation in domestic environments may constitute a real problem in public health and hygiene which lead to infections, allergies, … and particularly, respiratory illnesses.One of the most relevant example is Legionella, ubiquitous bacteria responsible of Legionnaires’ disease and Pontiac fever which are widely distributed in aquatic habitats (Morris et al., 1979). The occurrence of Legionella in water is well-documented. Paradoxically only few studies have been performed on the measurement of Legionella in aerosols generated using contaminated water. At present, the management of this biological risk only depends on the microbial water quality control.In this contexte, the metrological aspects, i.e.adapted metrological and analytical tools for Legionella detection, need to be improuved in order to perform an exposure assessment.For this purpose, we have performed a study in order to test and compare (1) three tools for bioaerosols sampling : impactor , impinger and filtration and (2) two detection methods for airborne Legionella : culture method and in situ hybridisation with fluorescent probe.The assays have been performed (a) in laboratory using an aerosol chamber to work with a controlled and stable aerosol of Legionella and (b) also in a health institution contaminated with Legionella to characterise the aerosol of Legionella generated by a shower head.The laboratory assays lead to the conclusions that the efficiency of the impinger is 4 and 800 times greater than the impactor and filtration sampling, respectively. Moreover, the results obtained in field conditions lead to the same ranking of the tested biosamplers for Legionella detection.Concerning the field assays, over a period of 6 months and in a real condition of exposure, airborne Legionella can be detected by FISH method when using the impinger (from 102 to 104 FISH cells/L) ; but no airborne Legionella were detected using the impaction technique.These assays offered a new approach to detect Legionella in aerosols by whole cell in situ hybridisation (FISH), leading to more realistic information of the human exposure to this bacteria