Since RI can be caused by too low of temperatures, a fan blowing across a screen top enclosure could cause the temperatures to fall, which could cause the RI.

Oooor a fan blows germ- or some other type of poluted- air (caustic chemically stuff?) into the enclosure...things that *can* cause RI.

From what I've read, RI can be caused by a number of things, but it seems the biggest cause is improper husbandry.