Syndromic Surveillance and Bioterrorism-related Epidemics

facilitate rapid detection of a future bioterrorist attack, an increasing number of public health departments are investing in new surveillance systems that target the early manifestations of bioterrorism-related disease. Whether this approach is likely to detect an epidemic sooner than reporting by alert clinicians remains unknown. The detection of a bioterrorism-related epidemic will depend on population characteristics, availability and use of health services, the nature of an attack, epidemiologic features of individual diseases, surveillance methods, and the capacity of health departments to respond to alerts. Predicting how these factors will combine in a bioterrorism attack may be impossible. Nevertheless, understanding their likely effect on epidemic detection should help define the usefulness of syndromic surveillance and identify approaches to increasing the likelihood that clinicians recognize and report an epidemic. B ecause of heightened concerns about the possibility of bioterrorist attacks, public health agencies are testing new methods of surveillance intended to detect the early manifestations of illness that may occur during a bioterror-ism-related epidemic. Broadly labeled " syndromic surveillance , " these efforts encompass a spectrum of activities that include monitoring illness syndromes or events, such as medication purchases, that reflect the prodromes of bioterrorism-related diseases (1–9). The Centers for Disease Control and Prevention (CDC) estimates that, as of May 2003, health departments in the United States have initiated syndromic surveillance systems in approximately 100 sites throughout the country (T. Treadwell, CDC, pers. comm.). The goal of these systems is to enable earlier detection of epidemics and a more timely public health response, hours or days before disease clusters are recognized clinically, or before specific diagnoses are made and reported to public health authorities. Whether this goal is achievable remains unproved (4,5,10). Establishing a diagnosis is critical to the public health response to a bioterrorism-related epidemic, since the diagnosis will guide the use of vaccinations, medications, and other interventions. Absent a bioterrorism attack, predicting whether syndromic surveillance will trigger an investigation that yields a diagnosis before clinicians make and report a diagnosis is not possible. Our objective is to consider the mix of hypothetical factors that may affect the detection of epidemics attributable to CDC category A bioterrorism agents (11). Establishing a Diagnosis Two pathways to establishing a diagnosis are described by the scenarios below and in Figure 1, using a single, clandestine dissemination of an anthrax aerosol as an example. The early signs of inhalational anthrax include nonspe-cific symptoms that …