Ricin is not contagious - only the people originally exposed would get sick. There's no fever, high or otherwise. The symptoms begin within hours of exposure. The symptoms are much more similar to anthrax, but again, anthrax isn't spread from person to person and could have been detected by nasal swabs relatively quickly.

The fact that this IS spreading indicates it's an infectious agent, although as MMario said, not a very infectious one. If I were to play arm-chair epidemiologist, I think the biggest clue would be looking for what it's hardest/more time-consuming/not likely to test for.