The Ghost Map: The Story of London's Most Terrifying Epidemic - And How It Changed Science, Cities and the Modern World by Steven Johnson
This book covers a very specific epidemic of cholera in London, and the reason the title calls it the most terrifying has less to do with the death toll as much as the quickness. While there are many epidemics had more deaths, few acted this quickly or this violently. One of the reasons behind this was partially related to urban development. It is also important to note that with the medical and scientific tools of the day, people had very different ideas of what caused diseases. While now it is common knowledge that cholera is spread through ingesting feces, commonly through contaminated water, at that point in time, people weren't aware of all the microbes in the water, and would assume it was clean just on appearance. There was also a large group of people that believed in the dangers of smell - people got sick because of the bad smell, not because of something like bacteria. Sometimes, the things done to get rid of smells actually made it easier for bacteria and viruses to spread.
Unfortunately, it's been a few months since I read this, so I'm a bit blurry on the details. It's easier for me to recall plots of novels than bits of scientific info, but I will say I thought the book was fascinating while I was reading it - very approachably written. Not only does the book discuss this epidemic, but it shows how this epidemic led to a greater use of statistics and maps to help argue the doctor's point. One doctor realized that it was the water supply that was at the source of the infection, and a reverend that actually disagreed with him ended up doing the ground work and the majority of the analysis on the spread of the disease. He ended up proving the doctor's point, and becoming an advocate for this type of research - and the doctor and his legacy. For example, the clergyman didn't just show which water point was closest but walked the route to determine which ones really were - for example, certain obstacles may have made others more convenient than one would suspect at first glance.
The only thing Johnson lost me on was in the last few pages when he used this to launch into a discussion on the future of cities. I thought some of the points were interesting but the author made a few too many broad, sweeping statements for my taste. However, as far as the rest of the book, it was an outstanding summary of a disease and the scientific method, and it also did a very good job of explaining the beliefs of the day that the doctor had to fight against. It would only be many years later that he would get any credit for his findings and accomplishments.