Describes the type of information that will be obtained (using a particular surveillance activity) about a health hazard. The options are early detection/warning of known (exotic or re-emerging) or unknown (new) disease; substantiate freedom from disease or infection; describe the baseline level, distribution, and impact of specified disease(s); describe changes in the health of the population (including changes in health indicators or in the incidence of specified diseases); describe changes that might threaten the health of the population; and detect cases to facilitate control.