Although many human infections are acquired from other humans, many are also the result of human interactions with their environment.
Pneumonia caused by Legionella bacteria (Legionnaires’ disease) is a notifiable disease of public health importance. New Zealand has the highest reported incidence of Legionnaires’ disease in the world, and our research has documented the high burden of this disease and the importance of sporadic (non-outbreak) disease. Legionella are environmental bacteria, and human disease follows various water or soil exposures.
A large proportion of cases of Legionnaires’ disease in New Zealand occur sporadically associated with gardening activities in spring and summer; exposure to compost-related products is an important risk factor. In contrast, outbreaks of Legionnaires’ disease are typically due to exposure to water sources (often created by humans) that are contaminated with Legionella bacteria.