I may be one of the last people in Portland to read this (Mark hasn't yet, ha!), because it was 2010's selection for the "Everybody Reads" program. (I think the name basically explains it, but the idea is that everyone in Portland reads the same book, and even if they don't attend discussions or anything like that, we're drawn together more as a community. Oh Portland.)
The book chronicles the last major outbreak of cholera in London, and its wide-ranging impact. It's a fascinating portrait of Victorian society and the evolution of scientific inquiry. As a person with a thoroughly literary, non-scientific mind, it was interesting acknowledging how certain things that I find to be natural and intuitive about science were completely ignored not so long ago (scientific method, anyone?). In the last two chapters, Johnson relates the epidemics of old to modern threats to civilization and their likely outcomes. It made me feel more sanguine about mass death and apocalypse. Perhaps not a great thing, but it was obscurely comforting to see the course of history as a continual pattern of overcoming and being brought down by tragedy.
The writing was engaging, I learned stuff, it was good.