An outbreak is defined as the unexpected occurrence of two or more cases of a disease in a given area, or among a specific group of people, over a particular period of time. For an outbreak to happen, the basic elements of disease causation involving agent, host and environment, together with a chain of transmission must be in place. A well established surveillance system enables us to observe and predict dangers posed by the outbreak and to understand the factors contributing to its spread. In responding to outbreaks of public health importance, the primary objective is to break the chain of transmission. Speed and accuracy are essential to managing the outbreak, and the epidemiological approach involves a systematic series of steps. One important determinant of success or failure is communication of the epidemiological findings and actions taken to the public and all those who need to know.