Legionnaires' is on the march

It's peak season for a potentially fatal respiratory disease linked to garden products. But there are ways to minimise the risks.

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Spring and early summer is a time for many New Zealanders to get outdoors and do some gardening. As a result, this is when we tend to see the most cases of legionnaires’ disease in this country.

“I always say that when the daffodil season starts then we’re preparing for the legionella season,” says Steve Chambers, a University of Otago respiratory and infectious diseases specialist.

Much of the problem has been traced to commercially produced potting mixes, soils and composts, which house a strain of bacteria known as Legionella longbeachae. When gardeners open the bags and inhale the contaminated dust, an infection can occur, particularly if they are older and have a compromised immune system or lungs.

Digging a home compost pile isn’t without risk, but bagged soil and composted plant material seem to provide a particularly welcoming environment for these organisms to flourish.

"A bag of compost has often been sitting in the sun on pallets covered with plastic and it creates a hothouse environment,” says Chambers.