top three:

1. the ghost map: the story of london's most terrifying epidemic - and how It changed science, cities, and the modern world - steven johnson (299 pages)
   subject: 1854 london cholera outbreak & the birth of epidemiology
   i cannot recommend this book strongly enough. it takes place in an era where most people thought that disease was caused by bad air - like, they thought that pumping sewage into the river thames to get it off the streets was a solid public health measure and bragged about how successful they were at it. (really.) this is, of course, not the case at all - cholera is spread by contaminated water - but convincing most medical professionals of that was a hell of a job. the story of dr. john snow and the broad street pump is pretty legendary if you're interested in this kind of thing - it's effectively a core starting point of the field of epidemiology as we know. the author really presents it in an accessible way and works in a lot of the intricacies and context around it that really help make the story clear. if you're at all interested in how the study of infectious disease works, this is a great starting point.
    
2. get well soon: history's worst plagues and the heroes who fought them - jennifer wright (336 pages)
   subject: overview of a number of different epidemics
   the ghost map barely beats this one out, and mostly does because of how significant it is as an introduction to the entire field of epidemiology and infectious disease. get well soon (which does have a chapter on the broad street epidemic) is just really, really fun - the author inserts a lot of witty, snarky commentary  (e.g., "you should not, for instance, decide diseased people are sinners and burn them at a literal or metaphorical stake, because it is both morally monstrous and entirely ineffective") that makes this super engaging and relatable. i really, really love it.
    
3. patient zero: a brief history of the science stories behind the world's worst diseases - lydia kang, nate pedersen, hillary huber (352 pages)
   subject: overview of a number of different epidemics
   a patient zero is where an outbreak starts, and this (like get well soon about) is a great overview of a lot of different outbreaks of infectious disease told in a really witty, accessible way. while there's a little overlap, they have different focuses, and i don't think it's enough to not make both books worth reading. patient zero was also published very recently, which means that it includes a chapter on covid-19, which i thought they handled really really well and in a way that's not going to mean that the book ends up becoming dated by, like, next year.

honorable mention:

the great influenza: the story of the deadliest pandemic in history - john m. barry (546 pages)
subject: 1918 influenza pandemic
this book is long and can get a little dry at times, but it's a really solid introduction to the 1918 pandemic as it existed in the united states. the title isn't exaggerating - it's estimated that the 1918 pandemic infected about a third of the global population and killed 50 million people (and maybe as many as 100 million), and unusually for the flu, the group it struck the hardest were young adults - which was particularly devastating given how much the war forced them into being in very close proximity. the impact it had on the war (and vice versa) is both fascinating and pretty heartbreaking - it's definitely worth reading up on.