Fever 1793 is a work of historical fiction by Laurie Halse Anderson concerning a widespread illness known as "Yellow Fever" spread by infected mosquitoes that many people in Philadelphia, Pennsylvania contracted during the summer of 1793. Summaries of each chapter of the book can be found here: http://www.enotes.com/topics/fever-1793.
Varying reasons contributed to the devastating affect of this fever, including hot, humid weather and the lack of medical knowledge and expertise concerning treatment of the illness.
At the time, the fever was incorrectly regarded as contagious between humans and resulting from "rotting vegetable matter" (see the Harvard link below). Because of this misunderstanding of the nature of yellow fever, treatment rarely proved effective, and many who contracted the sickness died.
Mattie Cook, the main character in the book, fears contracting the fever, grieves over deaths of those she loves because of the fever, and is in danger from those seeking to profit from the social and economic upheaval the fever incurs. While the book is a work of fiction, the context of yellow fever ravaging Philadelphia in 1793 is a historical fact. The author incorporates many true anecdotes that occurred because of the fever and creates believable characters in this gripping story.