Investigator-initiated active collection of animal health related data from individual units in a population which is not limited to a particular time period, to assess the disease status within the population. This can be carried out using a sample of the population of interest or using a census of all units. Some examples are: abattoir surveillance, ongoing self-monitoring by producers, pre-entry testing. Continuous monitoring is often used for case detection to facilitate control and for food-borne diseases.