查韦氏英语词典:
endemic: 1. growing or existing in a certain place or region.
2. common in a particular area or field.
epidemic: an occurrence in which a disease spreads very quickly and affects a large number of people.
按这样的解释:endemic指地方性流行,没有时间限制,强调地方性;epidemic指在某一特定的时间爆发流行,影响许多人,不受地域的限制,而强调时间的突然性。
不知上述解释是否符合您需要的含义?
也查了几本英汉、汉英词典,对这两个词的辨别比较模糊,固未采纳。