IOM defines an emerging infectious disease as either a newly recognized, clinically distinct infectious disease or a known infectious disease whose reported incidence is increasing in a given place or among a specific population. More than 36 newly emerging infectious diseases were identified between 1973 and 2003, and new emerging infectious diseases continue to be identified. Figure 1 provides information on selected emerging infectious diseases compiled by the World Health Organization (WHO) and CDC. According to CDC, nearly 70 percent of emerging infectious disease episodes during the past 10 years have been zoonotic diseases, which are diseases transmitted from animals to humans. The West Nile virus, which was first diagnosed in the United States in 1999, is an example of a zoonotic disease. The West Nile virus can cause encephalitis, or inflammation of the brain. Mosquitoes become infected with West Nile virus when they feed on infected birds, and infected mosquitoes transmit the virus to humans and animals by biting them. Other zoonotic diseases include SARS, avian influenza, human monkeypox, and variant Creutzfeldt-Jakob disease (vCJD), which scientists believe is linked to eating beef from cattle infected with bovine spongiform encephalopathy (BSE) and is also called mad cow disease. Surveillance for zoonotic diseases requires collaboration between animal and human disease specialists. Disease surveillance provides information for action against infectious disease threats. Basic infectious disease surveillance activities include detecting and reporting cases of disease, analyzing and confirming this information to identify possible outbreaks or longer-term trends, and applying the information to inform public health decision-making. When effective, surveillance can facilitate (1) timely action to control outbreaks, (2) informed allocation of resources to meet changing disease conditions and other public health threats, and (3) adjustment of disease control programs to make them more effective. In the United States, responsibility for disease surveillance is shared— involving health care providers; more than 3,000 local health departments including county, city, and tribal health departments; 59 state and territorial health departments; more than 180,000 public and private laboratories; and public health officials from four federal departments. Although state health departments have primary responsibility for disease surveillance in the United States, health care providers, local health departments, and certain federal departments and agencies share this responsibility. In addition, the United States is a member of WHO, which is responsible for coordinating international disease surveillance and response efforts. Health care providers are responsible for the medical diagnosis and treatment of their individual patients, and they also have a responsibility to protect public health—a responsibility that includes helping to identify and prevent the spread of infectious diseases. Because health care providers are typically the first health officials to encounter cases of infectious diseases—and have the opportunity to diagnose them—these professionals play an important role in disease surveillance. Generally, state laws or regulations require health care providers to report confirmed or suspected cases of notifiable diseases to their local and/or state health department. A notifiable disease is an infectious disease for which regular, frequent, and timely information on individual cases is considered necessary for the prevention and control of the disease. States publish a list of the diseases they consider notifiable and therefore subject to reporting requirements. According to IOM, most states also require health care providers to report any unusual illnesses or deaths—especially those for which a cause cannot be readily established. States, through the use of their state and local health departments, have principal responsibility for protecting the public’s health and therefore take the lead in conducting disease surveillance and supporting response efforts. Generally, local health departments are responsible for conducting initial investigations into reports of infectious diseases. They employ epidemiologists, physicians, nurses, and other professionals. Local health departments are also responsible for sharing information they obtain from providers or other sources with their state department of health. State health departments are responsible for collecting surveillance information from across their state, coordinating investigations and response efforts, and voluntarily sharing surveillance data with CDC and others. Several federal agencies and departments are involved in disease surveillance. For example, CDC, an agency in HHS, is charged with protecting the nation’s public health by directing efforts to prevent and control diseases and responding to public health emergencies. It has primary responsibility for conducting national disease surveillance and developing epidemiological and laboratory tools to enhance disease surveillance. CDC also provides an array of technical and financial support for state infectious disease surveillance efforts. FDA, which is also a part of HHS, is responsible for protecting the public health by ensuring that domestic and imported food products (except meat, poultry, and certain processed egg products) are safe and properly labeled. It is also responsible for ensuring that all drugs and feeds used in animals are safe, effective, and properly labeled and produce no health hazards when used in animals that produce foods for humans. FDA enforces food safety laws by inspecting food production establishments and warehouses and collecting and analyzing food samples for microbial contamination that could lead to foodborne illnesses. USDA is responsible for protecting and improving the health and marketability of animals and animal products in the United States by preventing, controlling, and eliminating animal diseases. USDA is also responsible for regulating veterinary vaccines and other similar products. USDA undertakes disease surveillance and response activities to protect U.S. livestock, ensure the safety of international trade, and contribute to the national zoonotic disease surveillance effort. In addition, USDA is responsible for ensuring that meat, poultry, eggs, and certain processed egg products are safe and properly labeled and packaged. USDA establishes quality standards and conducts inspections of processing facilities in order to safeguard certain animal food products against infectious diseases that pose a risk to humans. DOD, while primarily responsible for the health and protection of its service members, contributes to global disease surveillance, training, research, and response to emerging infectious disease threats. DHS’s mission involves, among other things, protecting the United States against terrorist attacks. One activity undertaken by DHS is to coordinate the surveillance activities of federal agencies and departments related to national security. While national governments have primary responsibility for disease surveillance and response within their country, WHO plays a central role in coordinating international surveillance and response efforts. An agency of the United Nations, WHO administers the International Health Regulations, which outline WHO’s role and the responsibility of member states in preventing the global spread of infectious diseases. Adopted in 1951 and last modified in 1981, the International Health Regulations require, among other things, that WHO member states report the incidence of three diseases within their borders—cholera, plague, and yellow fever. There are currently proposed revisions to these regulations that will expand the scope of reporting beyond the current three diseases to include all events potentially constituting a public health emergency of international concern. WHO is the agency that serves as the focal point for international information on these diseases as well as others, and the agency also helps marshal resources from member states to control outbreaks within individual countries or regions. In addition, WHO works with national governments to improve their surveillance capacities through—for example—assessing and redesigning national surveillance strategies, offering training in epidemiologic and laboratory techniques, and emphasizing more efficient communication systems. Disease surveillance comprises a variety of efforts at the state and federal levels. At the state level, state health departments collect and analyze data on notifiable diseases submitted by health care providers and others, although the diseases considered notifiable and the requirements for reporting them vary by state. State-run laboratories conduct testing of samples for clinical diagnosis and participate in special clinical or epidemiologic studies. State public health departments verify cases of notifiable diseases, monitor disease incidence, and identify possible outbreaks within their state. At the federal level, agencies and departments collect and analyze surveillance data gathered from the states and from international sources. Some federal agencies and departments also support their own national surveillance systems and laboratory networks and have several means of sharing surveillance information with local, state, and international public health partners. Finally, some federal agencies and departments support state and international surveillance efforts by providing training and technical expertise. To conduct disease surveillance at the state level, state public health officials collect reports on cases of notifiable diseases from health care providers and others. Both the diseases considered notifiable and the requirements for reporting them vary by state. Most states have their list of notifiable diseases approximate a national list of notifiable diseases maintained and revised by the Council of State and Territorial Epidemiologists (CSTE) in collaboration with CDC. (See table 1 for the 2004 national list of notifiable diseases maintained by CSTE.) This national list is reviewed annually and revised periodically. State lists of notifiable diseases generally include cholera, plague, and yellow fever—consistent with WHO’s International Health Regulations. On the other hand, according to state and federal health officials, states modify their list of notifiable diseases to reflect the public health needs of their region. States may include diseases on their state list that impact their state but do not appear on the national list. For example, one border state includes the gastrointestinal disease amebiasis—a disease most often found in the United States among immigrants from developing countries—in its state list of notifiable diseases. However, amebiasis is not included on the current national list of notifiable diseases. Conversely, states may exclude diseases that are on the national list but have little relevance for their state. For example, although Rocky Mountain spotted fever is listed on the national list of notifiable diseases, it was excluded from one state’s list we reviewed because relatively few cases of this disease are reported in that area. Appendix II provides a description of diseases on the national notifiable disease list and other selected emerging infectious diseases. States also vary in their requirements for who should report notifiable diseases, and the deadlines for reporting these diseases after they have been diagnosed vary by disease. Officials from the 11 states we interviewed told us that, in addition to health care providers, they require clinical laboratories to report notifiable diseases. On the other hand, some—but not all—of the11 states have expanded the responsibility for reporting suspected notifiable diseases.