In 1999 the Department of Defense-Global Emerging Infections System (DoD-GEIS) developed a prototype system for early detection of infectious disease outbreaks at military treatment facilities (MTFs) in the National Capital Area. Currently ESSENCE (Electronic Surveillance System for the Early Notification of Community-based Epidemics) collects data from over 300 MTFs world-wide. For every outpatient encounter within the DoD, diagnoses from the International Classification of Diseases, 9th Revision (ICD-9) are coded along with the patient's disposition and other data. In an effort to provide near real-time information, data is sent from MTFs to a centralized server where the DoD-GEIS can securely access and analyze the data. Similar ICD-9 codes are grouped together into syndrome groups that best represent presenting signs, symptoms and diagnoses of potential infectious disease outbreaks. Daily counts, ratios and syndrome-specific graphs are automatically updated and available on a secure website. The data is accessed and analyzed using commercially available software. However, the software is not Open Source, and the data is not sharable due to privacy restrictions. ESSENCE has detected many individual outbreaks as well as simultaneous outbreaks in different geographic areas and is expanding to include other data sources such as pharmacy prescriptions.