In my Troll Wife story, I mention "The Plague Wars". This was a war between the faeish and the humans, and was the first historical example of biological warfare on a massive scale.
I don't go into much detail about the Plague Wars in the story. If I took all the bits about the wars that are spread throughout the book and put them all together, it would be about 3 pages worth of stuff. That includes dialogue.
I did study the plague, (online articles and Discovery Channel documentaries) and also read "Return of the Black Death, The World's Greatest Serial Killer". Fully 3/4 of that book was about the symptoms of the disease.
Just as a side note, after reading Return of the Black Death, I agree with the authors that it wasn't the bubonic plague. There are similar symptoms, of course, but the incubation period doesn't match at all. And some of the worst hemorrhagic symptoms don't match. Plus the disease vector for the bubonic plague didn't even exist in some of the worst hit areas.
Anyway, other than the mention of the CCR5 gene and the death toll, none of that plague research ends up in the book. But I still needed to do it, so that I would know that what I did include was authentic and verifiable. I think it makes the stuff I made up seem more believable. I could be wrong :)
But lets face it, it was fun. If it weren't fun, I wouldn't have done nearly as much research. And as an added bonus, if anyone around me starts exhibiting symptoms of the Black Death, I'll know it right away!