A new study shows Legionnaires' disease is far more common than previously thought.
Canterbury researchers say many cases diagnosed as pneumonia are actually Legionnaires' disease.
Professor David Murdoch says they are systematically testing for the disease and are finding quadruple the number of cases previously recorded.
Professor Murdoch says Legionnaires' is just another kind of pneumonia but it is caused by a particular bacterium, which requires a specific antibiotic treatment.
He told Morning Report most of the cases have a link with gardening activities but the exact link and how to prevent the disease is still not known.
"We are planning a lot of activities from now on to try to pin that down," he said.