Nerundill caught hints, snippets of conversation. The rumors surrounded a book, a book of magnificent power. A book that contained the knowledge of the ancients. With every new tantalizing bit of information he heard, his resolve to possess this book increased.
When was the last time a character caught a cold or flu? Real people get them every now and again even with solid heating and dry interiors. Your characters are out in the cold and wet, and even inside is not always dry and warm. Imagine having to stop your dungeon crawl, sitting in a tight defensive position, while you all are feverish.