I agree with pathdr2be. While epidemiology at various levels may be complicated, it is not nearly as complex as the basic molecular sciences. An undergraduate course in statistics and some research experience is ample preparation for entry into an epidemiology program. That being said, some public health students take molecular-based courses in virology and bacteriology, for example, which take on more of a scientific bent and would be considered good preparation for medical school.
Epidemiology, however, assumes limited prerequisite knowledge of "how diseases work" and thus does not require much of a molecular science background that is essential in medicine. Screening, testing, surveillance, methodology, data collection, and interpretation (to name a few) are the essential functions of an epidemiologist.
Nevertheless, public health is a fascinating field that offers several opportunities to graduates. I am currently an MPH student and am interested in applying to medical school. Public health has broadened my perspective regarding medicine insofar as it has allowed me to appreciate the role of prevention, nutrition, health administration, health law and ethics, occupational safety, epidemiology and biostatistics, and environmental health in modern medicine. If you have an interest in any of these areas, public health may be a field worth pursuing. 🙂