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.