Review of The Ghost Map by Steven Johnson (Riverhead Books, 2006)

1854, London. Over the course of a couple of weeks Cholera sweeps through a Soho neighbourhood killing hundreds of people and sending others fleeing. Cholera is a relatively recent import from India and like other deadly ailments it is not well understood, thought to spread via foul-smelling vapours. Dr John Snow, a noted physician and anaesthetist, who lives close to the outbreak has a different theory which he has been working on for a number of years. He believes Cholera thrives in polluted water. The most recent outbreak gives him an opportunity to prove his case. One of his key methods is to plot the locations of deaths and the sources of drinking water. What his resulting map reveals is that Cholera victims are concentrated around a single water pump. While few share his conviction that Cholera is spread via drinking contaminated water, the local authorities do close the pump. His findings are confirmed by a local churchman, who determines that the victims did all drink from water collected from the pump and those that sourced their water elsewhere were unharmed. Despite the weight of evidence, some public health officials continued to believe the miasma theory rather than Snow’s conviction, but over time Snow’s map and data changed how cities were managed, with a vast public sewer network being built to separate drinking water from waste.

The Ghost Map tells the story of how Dr John Snow, a London physician, solved the problem of how to tackle Cholera. Johnson starts his historical tale by setting the scene and in particular detailing the filth and stench of the city and the various professions who cleaned and recycled the city’s waste. In the absence of sewers and formalized waste management, human and animal faeces littered streets and basements. It was the foul-smelling stench – the miasma – of such waste that was thought to spread disease. Snow, however, had a different theory – disease was spread via contaminated water – and most of the book concerns Snow’s work. In particular, the narrative focuses on the 1854 cholera epidemic, its catastrophic outcome on a local community, how by plotting ghosts on a map Snow identified the source of the outbreak, changing both the practice of epidemiology and public infrastructure and public health provision of modern cities globally. It’s an interesting tale, but it is a little uneven in its telling, with an overextended focus on some elements that drifted into repetition, and underdeveloped on others, particularly the public health situation and response, and the evolution of thinking and practice in the years proceeding Snow’s work. And the final chapter on the spread of disease and viruses in the present day, as well as urban development, was a potted attempt to convert the lesson from the nineteenth century to the present that felt like an add-on and speculative. In addition, the lack of Snow’s maps and analysis, especially the key Voronoi one, seemed an important oversight. Overall, an okay read about an interesting case.