Legionnaires’ disease: Health NZ warns gardeners of dangerous disease that spreads from potting mix

Bagged potting mix and compost can contain Legionella bacteria which can cause Legionnaires’ disease - a type of pneumonia.

Gardeners are being warned of a dangerous disease that can spread from potting mix.

Legionnaires’ disease can be caught from bags or bulk loads of potting mix and compost. It is a type of pneumonia which can lead to a mild, flu-like illness or more severe symptoms.

Health New Zealand said there have been 108 cases of Legionnaires’ disease confirmed across the country this year and urged gardeners to take care.

There was a case in Horowhenua and two in Taranaki, but none have yet been recorded in Whanganui.

National Public Health Service medical officer of health Dr Cheryl Brunton said the disease could be severe and, in some cases, life-threatening.

“Bagged potting mix and compost can contain Legionella bacteria which, when breathed in, can cause Legionnaires’ disease.“

MidCentral medical officer of health Rob Weir said there had not been any cases in Whanganui over the past few years but warned “gardeners and anyone handling compost or potting mix should still take precautions”.

New Zealand has had more than 100 cases of the disease this year. Photo / NZ Herald

Whanganui-based author Phil Thomsen, who wrote the book The Practical Kiwi Gardener, said it was important not to let potting mix bags dry out which could increase the risk of Legionnaires’ disease.

“Potting mix can be used to spread on to the garden but also for re-potting indoor plants or outdoor pot plants.

“That is the time to be vigilant.“

Thomsen said because it was a windy time of year, there was more danger of the spores blowing around.

“If the potting mix is dusty, you certainly shouldn’t have the breeze blowing it towards you.“

Springvale Garden Centre general manager Gareth Carter said people needed to be aware of the disease but they should not be fearful of gardening.

“It’s just about taking precautions.

“The stupidest thing you could probably do is opening the bag of potting mix with your head right by the bag.”

If a bag of potting mix had been left in a shed, it could become hydrophobic or dry out which would make it more dangerous, he said.

“I guess it’s about buying what you need for the season, month or job that you’re doing, rather than storing loads of it.”

Gardeners are being warned to take care to protect themselves from Legionnaires' disease. Photo/file

Thomsen said he tried to make sure the soil was reasonably damp when he was cultivating or weeding his garden.

“There’s much less risk of the dust and spores being disturbed if the soil is reasonably damp.“

Carter said spring was the time people prepared to plant their summer vegetables such as tomatoes, capsicums, beans, lettuces and courgettes.

“In the next few weeks basically, if you’re going to grow a summer vegetable now is a good time to put it in.“

At the Springvale Garden Centre, workers were careful to never handle dry potting mix or to open bags with people close by.

Health New Zealand advice

• Work with potting mix or compost in a well-ventilated outdoor area
• Wear a well-fitting face mask - an N95 or respirator is best
• Wear gloves when handling potting mix or compost
• Open potting mix or compost bags carefully using scissors and open them away from your face
• Reduce dust by dampening down the potting mix or compost before using it
• Wash your hands thoroughly after handling potting mix or compost and before touching your face or removing your mask.

“Legionnaires’ disease is a very serious illness and following these simple steps can be life-saving,” Brunton said.

The illness is more common in older people, particularly people who smoke, or have poor immunity or a chronic illness.

A Health NZ spokesperson said there was typically a spike in cases of Legionnaires’ disease in spring that could be associated with increased gardening activity and warmer weather.

Symptoms could include a “flu-like” illness, with a dry cough, high fever, chills, shortness of breath, muscle aches, headaches and diarrhoea.

Health NZ advises people with these symptoms to contact their healthcare provider right away for advice and say they have been handling potting mix or compost.

Eva de Jong is a reporter for the Whanganui Chronicle covering health stories and general news. She began as a reporter in 2023.