Beware the perils of potting mix

Queensland Health is warning people to take care in the garden due to a three-fold spike already this year in reports of Legionnaires’ disease linked to handling soils or potting mixes.

So far, 88 cases have been reported, which is three times the average, with two tragically resulting in the death of the patient.

Legionnaires’ disease is caused by a naturally occurring bacteria in the soil – Legionella longbeachae. The bacteria can also be found in potting mixes and bags of compost as well.

If the bacteria is inhaled (with dust or water vapour) or gets into the mouth (say by touching your mouth with dirty hands) it can cause a lung infection, ranging from a relatively mild respiratory illness called Pontiac fever, to pneumonia (Legionnaires’ disease) which if left untreated may be fatal.

Not all those who come into contact with the bacteria become sick and symptoms will vary from person to person.

If you become infected with Legionella, you may get flu-like symptoms that can range from mild to severe. It can, however, be life-threatening to people who have health factors that increase their susceptibility.

Gardeners most at risk include smokers, the elderly and those with existing respiratory illnesses and weakened immune systems.

Soils, potting mixes and composts are rich in microrganisms, bacteria and fungi, most of which are beneficial, and sometimes essential, to having healthy soils for healthy plants.

But the conditions which promote a healthy soil ecosystem – moisture, warmth, nutrients – also mean that the undesirables like the Legionella bacteria (and others) are able to prosper.

There’s no way of physically telling if the soil or potting mix had Legionella in it. There’s no strange smell or it doesn’t look any different, so the best approach is to take precautions whenever you dig soil or pot up plants.

Here’s what the health authorities say you can do to limit your risk:

•  Wet down the potting mix and soils to
    reduce the dust.

•  Minimise the amount of dust when working in the garden.

•  Wear gloves and a dust mask when using potting mix or digging dry soils.

•  Water gardens and indoor plants using a gentle spray, this way water won’t
    splash off the soil and into the air.

•  Open bags of soil products slowly, away from the face.

•  Make sure the working area is well ventilated.

•  Wash your hands after handling potting mix or soil, and before eating, drinking or smoking.

•  If you develop a flu-like illness which is worsening, see your doctor immediately.

Interestingly, the Legionella longbeachae bacteria was only discovered in potting mix in 1989 in South Australia. Since then the bacteria has been found around the world in different bagged products.

Some suggest that a change from peat based potting mixes to wood based potting mixes may have contributed to the rise in soil-borne Legionnaires’ disease.

One study found that almost 80 per cent of bagged potting mixes tested contained the Legionella bacteria.

So taking a precautionary approach whenever you open and use a bag of potting mix or compost is probably the best approach.

Stay safe and enjoy your gardening.