ABSTRACT
Public health organizations gather data from a number of sources for their traditional surveillance activities. These include various surveys of populations and, most notably, reporting by hospitals and physician's offices. This chapter explores some of the traditional methods used for disease surveillance. The Centers for Disease Control and Prevention's National Notifiable Diseases Surveillance System (NNDSS) is one example of event-based surveillance. The NNDSS is used to illustrate the historical limits method for disease outbreak detection. The historical limits method compares the observed incidence of a particular disease from a current time period to incidence data from equivalent historical periods. For a disease that is rare, the observed disease rates may vary considerably, even in neighboring counties. Multiple choropleth maps can be used to show the change in disease rates across time and across space.
