Medical Officer of health Margot McLean told the Dominon Post there had been 13 cases of legionellosis, or legionnaire's disease, in the wider Wellington region this year, compared with nine last year. Five of those cases were in the past two months.

Four of the recent cases of the disease, which can cause anything from mild flu-like symptoms to severe pneumonia, were likely to have been caused by a specific strain of the disease usually found in potting soil mix, McLean said Monday.

The disease is often associated with air-conditioning systems as legionella bacteria, which cause the disease. While the bacteria can live in the system cooling towers, it is also widespread in water, soil, potting mix and compost.

McLean suggested taking precautions such as opening the bags away from the face, and if working indoors, ensure adequate ventilation.

Moistening the soil first will also minimize dust, the report said.