These efforts led ultimately to the global eradication of smallpox. The continued occurrence of cases of smallpox despite high vaccination coverage led to the development of a new strategy for smallpox eradication i.e., a wide circle of contacts around each case-patient was identified and vaccinated, creating a wall of immunity around the remaining patients. This was illustrated during the global smallpox eradication program. In addition, timely notification is necessary so that public health action can be taken to limit spread of disease. The occurrence of these cases may indicate the need for new prevention strategies, but in order to track the impact of any such strategies, surveillance data are essential. To achieve a goal of zero cases of a disease, aggressive efforts must be made to identify factors that allow cases to continue to occur despite the low incidence of disease. In disease elimination programs, the role of surveillance is different. Despite this limitation, these data remain useful because they are used primarily for monitoring trends in disease occurrence rather than for initiating public health action in response to each individual case. However, even when supplemented by laboratory-based reports, reporting in traditional passive surveillance systems remains incomplete. For diseases and conditions for which laboratory confirmation is routinely obtained, laboratory-based reporting has virtually replaced traditional provider-based reporting in many jurisdictions, because case ascertainment is far more complete. Traditionally, communicable disease surveillance programs have relied on passive reporting, in which reports are received from physicians and other providers. For the Nationally Notifiable Diseases Surveillance System (NNDSS), components include case reporting from the health care provider to public health officials in a jurisdiction, the public health case investigation, and case notification from a jurisdiction to CDC. This chapter describes surveillance for diseases in various stages of prevention and control and discusses surveillance indicators that have been developed to evaluate the appropriateness, completeness, accuracy, and timeliness of surveillance systems. Without adequate surveillance, elimination of vaccine-preventable diseases cannot be achieved and sustained. In advanced disease elimination and eradication programs, every case counts. In contrast, in disease elimination or eradication programs, routine surveillance activities are inadequate once the goal is near. In routine disease control programs, traditional, passive disease surveillance systems are usually adequate to meet program demands despite their limitations. Roush, MT, MPH Role of Surveillance in Disease Elimination Programs
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