Legionnaires’ disease: The gardening risk that can turn deadly; what you need to know

Prendeville, a keen gardener, had been potting flowers for summer when, three days later, she began experiencing flu-like symptoms.

“I started feeling sick, started feeling fluey, achy, sore throat,” she told the Herald.

Her doctor initially believed she had the flu, but within days, her condition deteriorated.

Prendeville was diagnosed with pneumonia and transferred to Christchurch Hospital, where her temperature became so high she suffered convulsions and worsening breathing before collapsing and being placed on a ventilator.

“They said to my husband to prepare for the worst because they didn’t know what was going on.”

Doctors struggled to establish what was causing her illness before finally asking whether she had recently been gardening.

Prendeville told them she had been using potting mix.

“They clicked straight away.”

She was given different medication and began improving within 24 hours.

Prendeville said public health officials later tested the potting mix at her home and found several strains of bacteria.

She spent another few days in hospital and said it took about a month to recover from the pneumonia.

Thirteen years on, she still gardens and uses potting mix, but now wears a mask and gloves, opens bags carefully outdoors and dampens the mix.

“Just be very cautious using it.”

For keen gardener Robin Wilson, Legionnaires’ disease has not been a once-in-a-lifetime experience.

The 48-year-old contracted the illness three times after handling compost, first while living in Christchurch and twice since moving to Invercargill.

Wilson said the first episode was in 2011, after his family moved following earthquake damage to their Christchurch home.

He was restarting a garden and sieving dry compost, putting him close to the dust.

A couple of weeks later, he developed a fever and tightness and pain around his lower chest and upper abdomen, followed by severe hot and cold spells and shaking.

“I just sort of brushed it under the carpet and thought I’d come right.”

His partner eventually insisted he go to hospital.

Wilson said scans showed a mass at the bottom of his lung and doctors asked whether he had recently been around potting mix.

He spent about a week in hospital receiving antibiotics before continuing intravenous treatment at home through a PICC line.

“It was a bit of an ordeal, really.”

Wilson said he contracted Legionnaires’ disease for a second time around 2016 after again handling dry compost.

His third bout was about three years ago after moving a large pile of dry compost with a friend.

“He grabbed a big shovel load of it and buffed it into his wheelbarrow, and this big bloom of dry dust just came straight over me.”

Both times he recognised the symptoms and went straight to hospital, making those episodes less severe than the first, he said.

Despite having gardened since he was 7, Wilson admitted he still sometimes skipped precautions.

“You’d think I would learn, yes, but I didn’t.”

He washes his hands after gardening and tries to wear a mask when handling dry compost for longer periods but sometimes skips precautions when doing a quick gardening job.

“It wouldn’t surprise me if I got it again because I’m so slack, really.”

Who is most at risk?

University of Otago respiratory and infectious diseases specialist associate professor Michael Maze said the risk of contracting Legionnaires’ disease and dying from it increased with age.

People over 60 were particularly vulnerable, along with smokers and those with diabetes, heart or respiratory conditions, or weakened immune systems.

“Even older people who consider themselves healthy are still at risk of Legionnaires’ disease.”

Maze said potting mix was the main source of infection in New Zealand, but other forms of Legionella bacteria could grow in warm water, including cooling towers, large building water systems and spa pools.

These could cause infection when contaminated water droplets were inhaled.

He said commercial potting mix appeared to pose a greater risk than homemade compost, potentially because pine bark and sawdust provided favourable conditions for the bacteria.

However, he recommended taking the same precautions with all compost.

Respiratory Foundation medical director professor Bob Hancox said Legionnaires’ disease could be particularly severe, with many patients requiring hospital treatment.

He said the illness could initially resemble flu but tended to worsen rather than improve.

People experiencing high fevers or difficulty breathing should seek medical attention, he said.

Diagnosis required tests to identify the bacteria responsible for the pneumonia.

What you need to know

How is it caught? By breathing in Legionella bacteria from contaminated soil products or airborne water droplets, including those from poorly maintained water systems and spa pools.Who is most at risk? Older adults, particularly those over 60, smokers, and people with chronic illnesses or weakened immune systems.What are the symptoms? Fever, cough and breathlessness. Early symptoms can resemble flu or other forms of pneumonia.When should you seek help? See a GP if fever and cough persist for more than a few days. Seek medical attention sooner for breathlessness, chest pain, confusion, dehydration or worsening symptoms.How can you reduce the risk? Wear gloves and a well-fitting mask when handling potting mix or compost, dampen dry material to reduce dust, and wash your hands thoroughly after gardening.

Rafaella Melo is a multimedia journalist with more than 10 years’ experience in Brazil. She spent two years reporting for Hawke’s Bay Today before joining the NZ Herald’s Christchurch team in 2026.