The CRJ is one of the only airliners that does not use recirculation of cabin air. Small volume of cabin plus 2 engines suplying bleed air. Also, the CRJ is just a stretched Challenger and that had an even smaller cabin.
Although I have no statistical data, it is well known in my company that the incidence of pilots coming down with colds and flu is lower on the CRJ pool than on our other aircraft that uses recirculated cabin air.