The emergent or newly reemerging disease model often relies on poverty as a contributing factor in the transmission of infectious diseases. But as Andrew Price-Smith has argued, affluence can also be a factor in the enhanced transmission of infection. Legionnaires' disease, first identified in 1976 as the cause of a novel disease outbreak in Philadelphia, fits the model of such a disease of affluence. The Legionella bacteria readily finds niches in the equipment and systems of the modern-built environment designed to deliver and store fresh water for the comfort of its inhabitants. Ubiquitous in freshwater sources around the world, the built environment constitutes a "better" world for Legionella population increase and is likely to facilitate expanding outbreaks of Legionnaires' disease.