Or, it could have come from a lab worker. I hadn't seriouly entertained this possibility until I read that as a matter of course, all government employees working on anthrax projects received vaccinations, which makes it a lot harder to find them by looking for someone who is sick from accidental exposure. Right now, I seriously think this is the most likely possibility.
Hate to shoot the theory about the wonders of this vaccine, but the anthrax vaccine is not for inhalation anthrax. Now, protective gear is something to consider.
I just wanted you to get the right FACTS.