you only need to cure that guy in quarantined part of poor area,and you've done the quest..
It didn't help. I gave the cure to Tibus and Cedric, then killed Tibus and gave the cure to Sarah. The main quest "Find a solution to plague problem in Rivertown" still isn't solved.
Someone once wrote something about reporting to commander Ralph about Dr. Elrath and his basement. Ralph doesn't have such speech option.
How will I find out the cause of the plague? Is it sth about the "strangely smelling" empty flasks found at the well?