The Pesthouse was a fairly good book. It was a book that (much like The Road) the end is from an unknown source. I think it might have been just general collapse of the same measure as what happened in Wolf and Iron. The action of The Pesthouse takes place so far after the fact that no one remembers or even thinks about what happened.
What is revealed about this world can be summed up in one word ... reversion. Society has gone back to the world as I imagine it would be experienced in perhaps the early 1800s. People don't know where illness comes from and have all manner of home remedies. Also the North American continent is no longer able to comfortably support people. Americans don't think of themselves as Americans just members of the town where they live.
The bulk of the book is spent travelling to the coast. They are attempting to make it to the coast so they can all back to England. On the way they find/describe/run across all manner of the detritus of the Golden Age of America (my phrase). The descriptions of some of this is so it is impossible to figure out what is being described. Other item are pretty simple to figure out because of the location they are seen.
The whole time I read the book I was wondering why they were on the journey in the first place. I mean sure some sort of a disaster had happened but the land wasn't dead. They could still fish for birds in the air and eat fruits. They could still raise crops and animals for food. To me it was just as if life had gone to a simpler time. The people in the book just couldn't accept life as it was.
On the entire journey to the coast they beset upon by villains and it leads the reader to think if they are avoiding the same sort of treatment by evacuating the country or if they are simply jumping from the frying pan and into the fire.
The book most reminded me of Blakely's Ark by Ian Macmillian. They are both books where diseases are the central focus and only the rudiments of science are known. Blakely's Ark is a bit hard to find but worth it.