I've been doing a lot of work lately with automated Abductive Inference, and medical diagnosis has been cited as one of the key uses of same. Perhaps there could be some opportunity to collaborate (everything I do is open source as well, btw). If you guys would like to talk, feel free to hit me up at [email protected]
https://github.com/gafmgafm/med
There are similar products but they are not open source, such as: http://apimedic.com/ and http://www.diseasesdatabase.com/