JOHN SNOW, THE BROAD STREET PUMP, THE GHOST MAP, AND CHOLERA In 2006, Steven Johnson’s book on London’s most terrifying epidemic was published (1), and in 2007, Sandra Hempel’s book on the same topic was published (2). London in 1854 contained 2.5 million people in its 30-mile circumference. The city stank because of the animal waste and open sewers. Cholera, which had been in India for hundreds of years and was common in people in caravans, military operations, pilgrimages, and sailing ships, reached England for the first time in June 1831 and again in 1853 and 1854. The cause of cholera, Vibrio cholerae, was unknown until it was isolated by Robert Koch in Egypt in 1883.