Legionnaires’ disease from potting compost is a real issue so do you know what precautions to take, Australia is ahead of the rest of the world in this instance in that they print handling precautions on the bags of compost.
These warnings state:
- Wear a face mask when handling soil, mulches, compost or growing media indoors or in windy conditions.
- Open the bag using a blade with care to avoid inhaling airborne growing media, i.e. slowly and away from the face.
- Moisten the contents of the bag on opening, by making a small opening and inserting a garden hose to dampen the growing media.
- Avoid potting-up plants in unventilated areas, such as enclosed greenhouses or sheds.
- Wear gloves.
- Avoid transferring growing media from hand to mouth (e.g. rubbing face with a soiled hand or glove). Always wash hands after handling growing media, even if gloves have been worn, as Legionella bacteria can remain on hands contaminated by growing media.
- Store growing media in a cool place, away from the sun.
- Keep soils and growing media damp.
- Avoid raising soil near evaporative coolers.
- Water gardens and composts gently, using a low-pressure hose.
- When handling bulk quantities of growing media or other soil products, follow procedures that minimise dust generation.
Various research papers point out that whilst the route of transmission to the human host is not fully understood the possibilities include hand-to-mouth, aspiration, or aerosolization.
Interestingly not only are Legionella supported in human and amoebic hosts but it appears that L. longbeachae have been shown to colonize and persist within the intestinal tracts of Caenorhabditis nematodes but did not invade surrounding tissue and were excreted as differentiated forms similar in structure to protozoan cysts. This study suggested that nematodes may serve as natural hosts for Legionella spp. and assist in their propagation throughout soil environments.
The risks associated with using composts and catching Legionnaires’ disease are extremely low, with over a billion bags of compost sold and only 6 cases over the last few years in the UK , but it shows that Legionella is more persistent in the environment than perhaps first thought.