VIDEO: Family wants answers
The tragic irony is that Professor Casadaban had been trying to develop a vaccine so that thousands of people around the world wouldn't die a painful, ugly death from a bacterial infection related to the plague. But it was that bacterium that appears to have killed him.
"We really thought he was so strong, we didn't see this coming at all," said Leigh Casadaban, daughter.
Not only did they not see it coming, but sisters Leigh and Brooke Casadaban say their father never knew what killed him.
"It was just so much of a shock, even the time he was in the ER, from the moment he got accepted to the time he passed away. We had no idea, we didn't even get to say goodbye to him," said Brooke Casadaban.
Malcom Casadaban was a professor of molecular genetics at the University of Chicago for 30 years.
For the past eight years, his daughters say, he'd been working with a strain of bacteria called yersinia pestis, trying to develop a stronger vaccine for the plague, once the world's worst health scourge.
The weakened strain he was using, however, isn't supposed to make healthy people sick.
And that is the big mystery now for investigators with the Centers for Disease Control and the state and city public health departments who've been looking for clues at the U. of C. labs.
"Was it a change in the organism, something about the person infected that made him uniquely susceptible? We don't really know the answers yet," said John Easton, University of Chicago Medical Center.
"It was hurtful because we remember our father as very healthy. He rode his bike to work, never smoked, never drank," said Brooke Casadaban.
Brooke and Leigh Casadaban say they're not satisfied with the answers they've been given so far.
How did their father, who had flu-like symptoms, enter the hospital a week ago Sunday morning and die 12 hours later with no one suspecting that it could be related to the plague?
Leigh, who is following in her father's footsteps, now attends her father's alma mater Massachusetts Institute of Technology, says it may be up to her to solve this.
"I plan to go to the lab to read his papers and notes and go and really understand what he was trying to do," said Leigh Casadaban.
Leigh and Brooke say they've been told that their father is the first person in the Chicago area to die from this bacterium, an infection that is usually cured with antibiotics. They say they're not eager to file a lawsuit. But they are wondering now if someone at the hospital or the university should have been able to spot this before it was too late.