this article describes the process by which some concepts of epidemiological surveillance are elaborated and turned into operational categories to comprise the so-called epidemiologial surveillance system for two specific diseases. the authors describe some epidemiological concepts and categories which were elaborated over the course of the smallpox eradication program and more recently in the poliomyelitis eradication program. such concepts and categories as outbreak containment, cross-notification, and case definitions are described as they fit into a series of actions which make up the epidemiological surveillance system. finally, it is worth noting that the description developed in this article is based on personal observations, since the authors participated in the smallpox eradication program in bangladesh and somalia as well as in the regional poliomyelitis eradication program in the americas.
