How many programs should I apply for

From IMG Wiki - International Medical Graduates USMLE and Residency Wiki TM

It depends... The better your profile matches the specialty, the fewer programs you need. It is also very important to find out upfront what a program requires from its applicants. Usually each program has specific requirements for USMLE scores, attempts, year of graduation, ECFMG certification, etc. In general, Application to Interview ratio varies from 5 to 20. In other words, if your profile is on a low part of the scale, you should expect about 5 invitations for 100 applications.