Detecting exposure to Legionella in the shower is now possible using a sampling method devised by scientists in France.

People can become infected with Legionnaire's disease if they breathe air contaminated with Legionella pneumophila  bacteria. However, the bacteria live in water and humid environments and until now, assessing the health risk they pose has relied on measuring their levels in contaminated water. 

Laurence Mathieu at the National Institute of Health and Medical Research in Nancy, and colleagues decided to investigate whether the concentration of Legionella  bacteria in water could be linked to their abundance in air.

Mathieu prepared aerosols from L. pneumophila-contaminated water samples and then collected the bacteria using a technique called liquid impingement. This method deposits the bacteria on a liquid surface, which prevents them from drying out. Mathieu measured the Legionella  levels of the resulting liquids using the fluorescent in situ  hybridisation, or Fish, method. Fish uses fluorescent DNA probes to bind to the DNA or RNA of a target species. By using a probe specific for the 16S RNA characteristic of Legionella sp. Mathieu was able to make the bacterial cells visible under a microscope.

Mathieu used his sampling method to measure L. pneumophila  concentrations in aerosols generated from contaminated hot-water showers. Whereas conventional culture techniques underestimate bacteria numbers, he said, combining the Fish method with liquid impingement achieved a significant detection rate. The method can detect bacteria present at a level of less than one hundred bacteria per litre of water. 

'Because there is no standard method of sampling and quantifying Legionella  and many other airborne microorganisms, this work is an important step in the attempt to reduce exposures to Legionella,' said Anne Mette Madsen a researcher at the National Institute of Occupational Health in Copenhagen, Denmark.

Janet Crombie