I've got a soft spot for books about deadly disease, when they're leavened with personalities and points of human contact. Ghost Map documents London's deadly 1854 cholera epidemic and the discovery, via innovative use of maps and creative thinking, that cholera is spread via contaminated water. Like the lantern overturned by Mrs. O'Leary's legendary cow, a single upended chamber pot started a cycle of rapid and terrifying death. Many factors aligned to instigate the epidemic: A single household's use of a front cesspool rather than the rear, that pool's proximity to a poorly lined well, and the tendency of that well's refreshingly tasty water to draw children and adults for blocks around. The single, dogged doctor who managed to pull the pieces together, John Snow, is artfully drawn as the sort of classic polymath made impossible by our current state of specialization and scientific progress. His triumph over the pseudoscientific theories of his fellows stands as testament to his genius, and one wonders what other discoveries he might have made given a long lifespan (Snow expired early, the price of his using himself as test subject).
The chief quarrel I have with this book is its pacing. Snow convinces authorities to remove the handle from the contaminated pump and the epidemic trails off. However, Johnson spends a few chapters after that establishing that the epidemic was petering out on its own, and that Snow's accomplishment with respect to lives saved as a direct result was arguably nil. After dampening our passion and excitement for Snow's victory for several dozen pages, though, Johnson reveals that the same household in which the epidemic began had one of its last victims. The disposal of bodily fluids from that victim would have reignited the disease and caused it to spread again through the neighborhood with lethal effect---had it not been for the pump handle's removal. Perhaps for someone who read this book in a more detached manner, this about-face would not have seemed as jarring.
The only other issue is that the closing chapter connecting Snow's mapping and discovery with the present day feels tacked on. An editor might have told Johnson that the story of the outbreak and those who fought against it stands just as well on its own, without need for didactic discourses on modern threats. But that is merely a quibble. Recommended.