Edgar was already showing symptoms of fever when he left his home in Virginia, he shook it off and decided to start his tear anyway. It was a fatal mistake. The alcohol that would be consumed later would have impaired his judgment, thus leaving him out in the cold and rain without protection from the elements. This would then cause inflation of the brain, which would then lead to its death. This point, while debatable, is a pretty strong theory. Without any protection from the elements, man would succumb to all the viruses and diseases that would result from being out in the cold for long periods of time without external protection. And in the time Poe lived, medical ability would not have been enough to compensate for any illness he might have had