Take precautions with compost and potting mix

17 November 2015


Take precautions with compost and potting mix

It is spring, so Aucklanders are outdoors preparing the garden for summer, or tending to the veggie patch. Medical Officer of Health Dr Simon Baker enjoys gardening as much as the next person, but he’s urging gardeners to take care with composts, potting mixes, and similar products.

“Composts and potting mixes are great for boosting plant growth, but they can also be fertile ground for one of the bugs that cause Legionnaire’s disease,” he says.

“Legionnaires’ disease is a serious illness, causing pneumonia, and usually requires hospital treatment. It has caused deaths in New Zealand that have been directly linked to potting mixes and composts,” Dr Baker says.

New Zealand has one of the highest incidences of Legionnaires’ disease in the world. This is probably because one of the rarer forms of the bacteria internationally, Legionella longbeachae, is the predominant species in New Zealand. This is the species most often found in potting mixes and composts.
In the last six months, 14 of the 37 cases of Legionnaire’s disease in the Auckland region were L. longbeachae cases. Auckland has had sixlongbeachae cases notified in the last two weeks, typical for this time of year.

The Canterbury region has the country’s highest incidence of Legionnaires’ disease. Fatalities in that region have prompted medical practitioners to assume Legionnaires’ disease is the cause of pneumonia in gardeners, until proven otherwise.

The legionella bacteria is contracted simply by breathing it in. Dr Baker advises gardeners take a sensible approach to avoid inhaling dust from potting mixes and composts. Gardeners can reduce the risk with a few simple precautions.

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

• Do your potting in a well-ventilated area, or outdoors, as you can breathe in Legionnaire’s disease bacteria
• Open compost bags carefully using scissors, rather than ripping them open
• When opening a compost bag, keep your head and face well clear. Open the bag slowly, and away from your face.
• Moisten dry compost before use. Dampen down dry compost heaps before turning or use.
• Water your plants using a gentle spray
• Avoid hand-to-mouth contact while gardening
• Wear gloves when handling compost. Thin latex (or latex-free for allergy sufferers) gloves can be worn for delicate work.
• Fold over and clip (e.g. with a clothes peg) the top of compost bags when not in use
• Avoid storing compost in greenhouses, as these will heat up, and may encourage Legionella bacteria to grow. Store bagged compost in a cool, dry place.
• Consider wearing a P2 dust mask when turning compost heaps and handling composts and potting mixes. These cost about $10 for a pack of three from hardware stores, but should be thrown away after a day in the garden.
• Finally, and most important of all, wash your hands thoroughly after handling compost or doing any gardening, even if you were wearing gloves
Anyone can catch Legionnaires’ disease but the most vulnerable are those over 50, those with a long-term illness, lung disease, low immunity or cigarette smokers.

Symptoms of the disease include:
• coughing
• high fever
• shortness of breath
• chest pains

“This is a lovely time of the year, but look after yourself in the garden,” Dr Baker says. “If you are unlucky enough to catch pneumonia, tell the doctor if you have worked in the garden in the last two weeks.”

Ends

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