It does seem to be more commonly (although not exclusively) seen in female runners, and I have a couple of possible explanations for this coming up. (exclusive.multibriefs.com)
The top three male and female runners overall were awarded with $ 1,000, $ 750 and $ 500 prizes. (mymoni.com)
Depending on the study, it is estimated that 40 - 75 % of female runners deal with incontinence. (gastownphysiopilates.com)