Legionnaires' disease was identified by astute and vigilant epidemiologists after men who had attended a convention of the American Legion in Philadelphia in 1976 succumbed to a lethal variety of pneumonia that resisted conventional antibiotics [21]. Retrospectively, earlier outbreaks in other places were identified. Legionnaires' disease is caused by Legionella pneumophilia, an elusive microbe that lurks in warm, moist environments, such as poorly maintained air conditioners and Turkish baths. The detective work that clarified the Philadelphia outbreak is a fascinating story.

Legionnaires' disease illustrates how the combination of what may have previously been an innocuous microbe and some of the inventions and technologies intended to add to the comfort of modern life can produce a dangerous brew. Comfort can have a high price.

Legionnaires' disease can kill. Lyme disease mostly just cripples. This disease carries the name of the town in Connecticut where it was identified in the 1970s [22]. Lyme disease is due to a spirochete, Borrelia burgdorferi. This is transmitted by ticks whose natural host is deer and other ungulates. B. burgdorferi may have been around for millennia. But something has changed recently to make this a human problem. Perhaps it is predator-prey relationships between deer and wolves: as predators decline, their prey proliferate. Perhaps it is encroachment of human settlements into the deers' habitat. Perhaps both or other processes are occurring.