ed States, including the intentional contamination of salad bars with Salmonella organisms in 1984 in Oregon (4) and of muffins and pastries with Shigella organisms in Texas in 1996 (5); these acts served as a wake-up call announcing the threat of domestic bioterrorism. All of these events led the United States to revisit and update a national plan for bioterrorism preparedness and response in the late 1990s. In defining the role of the public health community in the detection of and response to bioterrorism, the Centers for Disease Control and Prevention (CDC) identified 10 major areas of need. One of these areas is ensuring reliable and timely disease surveillance and reporting to detect and investigate outbreaks (6).
In response to global bioterrorism threats, CDC has proposed a list of critical biologic agents that have potential for use in a terrorist incident (6–9). This list includes a wide range of biologic agents and prioritizes pathogens into three categories on the basis of their potential to affect the public’s health, their potential for dissemination, and special needs for effective public health intervention. Prioritization of bioterrorism “threat” agents facilitates coordinated planning efforts for preparedness and response to bioterrorism at the local, state, and federal levels.
Using this guidance, public health systems can address the threat of bioterrorism by increasing healthcare sector awareness of and surveillance for these bioterrorism-related agents and the diseases they cause (10). In the United States, public health surveillance for conditions caused by the identified critical biologic agents is conducted in multiple ways. Although data regarding these agents are reported to different national surveillance systems at CDC, no single system is specifically designed for conducting surveillance for all bioterrorism-related agents or conditions. However, many states have routinely conducted surveillance for some of these conditions and report incidence data to CDC’s National Notifiable Diseases Surveillance System (NNDSS) each week (Table 1).
We describe disease-specific trends in demographic characteristics and geographic and seasonal distribution of selected conditions caused by critical biologic agents reported to NNDSS. These diseases and conditions include anthrax, botulism, brucellosis, cholera, plague, tularemia, and selected viral encephalitides. By identifying patterns of endemic disease associated with critical agents, we establish a baseline against which future disease incidence can be compared. This process should allow easier identification of unusual reports of disease incidence, which in turn will enhance the ability of the public health community to identify and investigate outbreaks.
Data and Sources
We analyzed NNDSS data voluntarily reported to CDC from state health departments from 1992 to 1999 (11). As of 1999, a total of 56 infectious diseases or conditions with public health surveillance case definitions (12,13) were considered nationally notifiable, as agreed upon by the Council of State and Territorial Epidemiologists and CDC (14). Each year, the Council and CDC review the list of nationally notifiable infectious diseases to determine whether conditions should be added or removed as new pathogens emerge or disease incidence changes (15). Based on state-specific health priorities, each state independently determines which of the nationally notifiable diseases should be made notifiable (i.e., legally reportable by healthcare providers or laboratories to the public health system within their jurisdiction). As a result, not all nationally notifiable diseases are legally reportable in all states. With some variation by jurisdiction, the completeness of public health surveillance is dependent on healthcare providers and laboratories submitting disease incidence or laboratory reports to local and county health departments, who then forward reports to the state health departments (16). Each week, health departments in 50 states, New York City (a separate reporting jurisdiction from