Public Health Surveillance

Public health surveillance is the continuous and systemic collection, analysis, interpretation, and feedback of systematically collected information used to inform public health decision making.22 Timely community health information in the hands of trained experts is the foundation for recognition of threats to health. To intervene successfully to treat existing infections and prevent the onset of new ones, disease surveillance systems need to provide a continuous, accurate, and near real-time overview of a population's health. Surveillance systems must be sensitive in terms of their ability to detect outbreaks and other significant changes in community health status over time, and they must be flexible in adapting to changing health intelligence needs. Given the increasing pace of international travel and globalization and the threat of intentional outbreaks, surveillance activities need to extend beyond the monitoring of disease burden to include the capacity to quickly recognize unusual, unexpected, or unexplained disease patterns. Because many emerging infectious agents are zoonotic, it is also important to integrate veterinary disease reporting networks into systems that monitor diseases of humans.

Astute clinicians and microbiologists are essential for early detection of threats at the clinical front lines. In the United States, surveillance for notifiable diseases is conducted by state and local health departments, which receive reports from physicians, nurses, and laboratorians who are often the first to observe and report unusual illnesses or syndromes. States voluntarily report nationally notifiable diseases to the Centers for Disease Control and Prevention (CDC) through the National Electronic Telecommunications System for Surveillance (NETSS). To expedite national disease reporting, CDC, in collaboration with the Council of State and Territorial Epidemiologists (CSTE), has developed a standards-based system for collecting and distributing electronic disease reports from local health departments to state and federal public health authorities. The infectious disease surveillance component of this developing Public Health Information Network (PHIN) is the National Electronic Disease Surveillance System (NEDSS). NEDSS is designed to standardize and facilitate the collection of electronic disease information on nationally notifiable diseases within local health jurisdictions directly from healthcare providers to local health authorities.23 Limited resources have, however, precluded the establishment of a fully integrated health surveillance system that connects health departments and care providers.

Starting in 1994, CDC launched a two-phase initiative to strengthen domestic capacity to respond to the dual threats of endemic and emerging infections. The publication of

FIGURE 15-1 Distribution of Emerging Infections Programs (EIPs), a network of state health departments and their collaborators in local health departments, academic institutions, and clinical settings, coordinated by the Centers for Disease Control and Prevention, 2004. Surveillance population: approximately 44 million.

FIGURE 15-1 Distribution of Emerging Infections Programs (EIPs), a network of state health departments and their collaborators in local health departments, academic institutions, and clinical settings, coordinated by the Centers for Disease Control and Prevention, 2004. Surveillance population: approximately 44 million.

two strategy documents24-25 led to the launching of new surveillance initiatives, including the Emerging Infections Program (EIP), a national network for population-based surveillance and research26 (Fig. 15-1). Several provider-based sentinel surveillance networks were established in collaboration with emergency room physicians, infectious disease specialists, and travel medicine specialists to provide early warning of events that might be missed by public health surveillance. Additional enhancements to the surveillance effort include development of the National Molecular Subtyping Network for Foodborne Disease Surveillance (PulseNet) as an early warning system for foodborne diseases, support for the Gonococcal Isolate Surveillance Project (GISP) to monitor antimicrobial resistance in Neisseria gonorrhoeae, strengthened surveillance for diseases of current concern (e.g., West Nile encephalitis), and surveillance for outbreaks that might be due to acts of bioterrorism.

The CDC also works in partnership with the World Health Organization (WHO), ministries of health, foundations, development agencies, and other federal agencies to promote national, regional, and international disease surveillance. Recognition of the global nature of the emergence and spread of infectious diseases stimulated the development of a third strategy document focused on CDC's efforts to enhance global capacity for disease surveillance and outbreak response.27 The document presents six priority areas for protecting domestic and global health, among which are global initiatives for disease control, international outbreak assistance, and a global approach to disease surveillance. CDC's international activities include creation of the United States-Mexico Border Infectious Disease Surveillance (BIDS) system, development of the Global Emerging Infections Sentinel Network (GeoSentinel), and provision of technical assistance to regional disease surveillance networks in Africa, Asia, Latin America, and the circumpolar regions of Canada and Europe, as well as to WHO's disease-specific global networks.

WHO manages global disease surveillance and response through a composite of partnerships and networks for gathering, verifying, and analyzing international disease intelligence, mainly to support global and regional efforts to eradicate certain diseases, such as polio, and to protect the global community against diseases with pandemic potential. The oldest of these networks is the global influenza surveillance network, which was established more than 50 years ago and has served as the prototype for the design and implementation of subsequent systems (see later discussion).28 A recent addition to the disease-specific surveillance approach is DengueNet, a web-based network for gathering and sharing information on dengue and dengue hemorrhagic fever.

To respond to the increasing number of emerging and rapidly spreading infectious diseases, WHO has developed a global "network of networks" that links local, regional, national, and international networks of laboratories and medical centers into a mega-surveillance network for early warning and response.29 Formal partners include ministries of health, WHO Collaborating Centers, WHO country and regional offices, and international military groups such as the Global Emerging Infections System of the U.S. Department of Defense (DoD-GEIS). Outbreak reports are also received from nongovernmental organizations, relief workers, private clinics, individual scientists, and public health practitioners. Additional information is provided by Health Canada's Global Public Health Intelligence Network (GPHIN), an electronic tool used by WHO since 1997, which scans Internet news sites for reports of outbreaks and unusual disease events.

Surveillance for Emerging Infectious Diseases and Bioterrorism Threats

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