If you enjoyed Stephen King's modern classic, THE STAND, (I believe King's best work) then you should read this book. The similarities are striking. Though this book was published five years prior to THE STAND, and garnered little notariety, I believe it may have been King's inspiration. Though I would hasten to accuse King of plagiarism, read this book and see what you think.
At under 300 pages, the story is not nearly as detailed or developed as King's work, but this makes for a quick, easy read over a rainy weekend.
Where THE STAND focuses on a viral infection which desimates the general population, this book features tiny microbial beings spread through airborne contact and, as the name implies, does nasty things to the human brain. The book also falls short of King's rendition of the struggle of good versus evil, but if you liked King's book, you may like this one even better.