Timeliness can be defined in various ways:Usually defined as the time between any two defined steps in a surveillance system. The time points chosen are likely to vary depending on the purpose of the surveillance activity. For outbreak detection this can be defined using various time points (e.g. the time between exposure to the infectious agent and the initiation of risk-mitigation measures or the time between when disease could have been detected and reported and the time when it actually was reported).For planning purposes, timeliness can also be defined as whether surveillance detects changes in time for risk-mitigation actions to reduce the likelihood of further spread. One way of measuring this would be to assess the number of cases present in the population when disease was detected.The precise definition of timeliness chosen should be stated as part of the evaluation process.