There has been a surge of people being treated for Legionnaire's disease at Christchurch hospital.
The Canterbury District Health Board said there had been 10 cases in the past two months.
Christchurch Hospital said of the ten cases of legionella pneumonia at least one person required treatment in intensive care.
It said nine of the patients who contracted the disease in October and November spent time gardening or were exposed to compost or potting mix.
Legionella was a bacterium commonly found in soil and organic soil mixtures.
It became dangerous when dust from affected products was inhaled.
Gardeners were advised to open bags with scissors rather than tearing them open, wear a disposable mask and gloves, do their potting outdoors, and wash their hands thoroughly after using a mixture.