These are generally offered as separate courses. Yes, they can be difficult, particularly if you have been away from studying for a time — as in practicing clinicians. read more
If you meant a single course in epidemiology perhaps in a nursing degree program, they can only really give you some basic principles of the field in the time permitted, but the opportunity is there to go on and apply for a graduate program (MSc, MPH, MHSc) in epi & biostats later. read more
On the other hand, if the biostatistics course is taught by a professor who focuses mainly on concepts, theories and ideas (e.g. relative risk, principles of epidemiology, percentage of patients who lose 100+ pounds after gastric bypass, etc), it's not too bad. read more
My intro epi course wasn't any harder than biostats, but I wasn't a fan of that professor so much. hard and easy are very relative terms most of the time. If you're looking for resources to prepare for a class you're already registered for, you could probably just email the professor. read more