When Batman activates the secret panel to enter the Chamber of the Demon, he deduces that a sword is required to open the door. But in the assembled footage previously shown, the assassin does not use her sword at all.
After infecting Batman with his poisonous blood, Joker says he had also shipped some all over Gotham, possibly infecting even more people. By the game's end, Batman manages to cure himself, but it is never mentioned if the other people in Gotham managed to be cured as well.
It is implied, however that the cure likely will be sent out to the other infected by way of mass producing the cure which is now within Batman's bloodstream.