It seems that the earliest way to contract vampirism is via random event after escaping Helgen (at the beginning of the game). If so, is there a consistent way to do it?
It is important to me that the means is legitimate, but information about less-legitimate means may still prove useful and I am willing to cheat to simulate optimal RNG.
Best Answer
There is a vampire cave if you head east into the mountains after leaving Helgan. Should be the road to Iverstead. http://elderscrolls.wikia.com/wiki/Haemar's_Shame