As developed nations continue to strengthen their electronic disease surveillance capacities [1], the parts of the world that are most vulnerable to emerging disease threats still lack essential public health information infrastructure [2,3]. The existing network of traditional surveillance efforts managed by health ministries, public health institutes, multinational agencies, and laboratory and institutional networks has wide gaps in geographic coverage and often suffers from poor and sometimes suppressed information flow across national borders [4]. At the same time, an enormous amount of valuable information about infectious diseases is found in Web-accessible information sources such as discussion sites, disease reporting networks, and news outlets [5,6,7]. These resources can support situational awareness by providing current, highly local information about outbreaks, even from areas relatively invisible to traditional global public health efforts [8]. These data are plagued by a number of potential hazards that must be studied in depth, including false reports (mis- or disinformation) and reporting bias. Yet these data hold tremendous potential to initiate epidemiologic follow-up studies and provide complementary epidemic intelligence context to traditional surveillance sources. This potential is already being realized, as a majority of outbreak verifications currently conducted by the World Health Organization (WHO)'s Global Outbreak Alert and Response Network are triggered by reports from these nontraditional sources [5,6].

In one of the most frequently cited examples [9], early indications of the severe acute respiratory syndrome (SARS) outbreak in Guangdong Province, China, came in November 2002 from a Chinese article that alluded to an unusual increase in emergency department visits with acute respiratory illness [9,10]. This was followed by media reports of a respiratory disease among health care workers in February 2003, all captured by the Public Health Agency of Canada's Global Public Health Intelligence Network (GPHIN) [10,11,12]. In parallel, online discussions on the ProMED-mail system referred to an outbreak in Guangzhou, well before official government reports were issued [13].

These Web-based data sources not only facilitate early outbreak detection, but also support increasing public awareness of disease outbreaks prior to their formal recognition. Through low-cost and real-time Internet data-mining, combined with openly available and user-friendly technologies, both participation in and access to global disease surveillance are no longer limited to the public health community [14,15]. The availability of Web-based news media provides an alternative public health information source in under-resourced areas. However, the myriad diverse sources of infectious disease information across the Web are not structured or organized; public health officials, nongovernmental organizations, and concerned citizens must routinely search and synthesize a continually growing number of disparate sources in order to use this information. With the aim of creating an integrated global view of emerging infections based not only on traditional public health datasets but rather on all available information sources, we developed HealthMap, a freely accessible, automated electronic information system for organizing data on outbreaks according to geography, time, and infectious disease agent [16] (Figure 1).

Operating since September 2006, HealthMap (http://www.healthmap.org/) is a multistream real-time surveillance platform that continually aggregates reports on new and ongoing infectious disease outbreaks [17]. The system performs extraction, categorization, filtration, and integration of these reports, facilitating knowledge management and early detection (Figure 2). Through this approach, we seek a unified and comprehensive view of current infectious disease outbreaks in space and time worldwide.

HealthMap is designed to provide a starting point for real-time intelligence on a broad range of emerging infectious diseases for a diverse range of end users, from public health officials to international travelers [18,19,20]. The system currently serves as a direct information source for approximately 20,000 unique visitors per month, as well as a resource for libraries, local health departments, governments (e.g., the US Department Health and Human Services and Department of Defense), and multinational agencies (e.g., the United Nations), which use the HealthMap data stream for day-to-day surveillance activities. Many regular users come from the WHO, the US Centers for Disease Control and Prevention, and the European Centre for Disease Prevention and Control.

A wide range of further improvements are currently being developed across all components of the HealthMap system. In particular, population and geography gaps in the coverage of the monitored sources need to be better understood and accounted for. For example, there are critical gaps in media reporting in tropical and lower-latitude areas, including major parts of Africa and South America—the very regions that have the greatest burden and risk of emerging infectious diseases (Figure 3) [3]. Monitoring other Internet-based sources such as blogs, discussion sites, and listservs could complement news coverage. The use of click-stream data and individual search queries is also a promising new surveillance source [24]. Multilingual surveillance is critical for capturing greater geographic coverage and for providing earlier and more comprehensive reporting from local news media.

Potential future challenges include the possibility that news data sources that are freely available now will no longer be available if current business models change. In addition, the way news is reported online (content, format, communication standards, etc.) may change and develop in the coming years, which will require a re-tooling of the system in order to capture the appropriate information. Potential future benefits of technological advances include better meta-data tagging if/when the semantic Web becomes a reality. Also, as location-based services become more widespread, including on portable devices, HealthMap feeds can be tailored and targeted to specific users and their locations.

Future work must also focus on improving natural language processing capability to clearly identify the pathogen, filter non-pertinent reports and duplicates, and enhance the spatial resolution of location extraction. However, while improvements in machine learning techniques are undoubtedly critical, they cannot currently replace human analysis. The success of Wikipedia has shown that leveraging collaborative human networks of trained public health professionals has the potential to support improved classification, severity assignment, conflict resolution, geocoding, and confirmation of reports on rare or unknown infectious diseases [25]. A recently established collaboration between HealthMap and ProMED-mail (http://www.healthmap.org/promed) is helping to pave the way for such a bidirectional system of classification and curation of information flow [26].

Continued system evaluation is also essential. The fundamental characteristics of different news source types need to be quantified, including sensitivity, specificity, and timeliness [27,28,29,30]. Consideration should also be given to integrating unstructured online information sources with other health indicator data to provide a broader context for reports. Pertinent data sets include mortality and morbidity estimates, laboratory data, field surveillance (e.g., vector and animal reservoir distribution), environmental predictors (e.g., climate and vegetation), population density and mobility, and pathogen seasonality and transmissibility. Such integration could yield a more precise relevance score for a given report, define populations at risk, and predict disease spread.

HealthMap is a member of a new generation of surveillance systems that mine media sources in near real-time for reports of infectious disease outbreaks, including GPHIN [10,12], MedISys, developed by the Directorate General Health and Consumer Affairs of the European Commission [31], the US government-funded Argus [32], and EpiSPIDER [33]. While Internet-based online media sources are becoming a critical tool for global infectious disease surveillance, important challenges still need to be addressed. Since regions with the least advanced communication infrastructure also tend to carry the greatest infectious disease burden and risk, system development must be aimed at closing the gaps in these critical areas. Hence, achieving global coverage requires attention to creating and capturing locally feasible channels of communication. It also involves making the outputs of the system more accessible to users in these regions through user interfaces in additional languages and low-bandwidth display options, including mobile phone alerts.

Ultimately, the monitoring of diverse media-based sources will augment epidemic intelligence with information derived outside the traditional public health infrastructure, yielding a more comprehensive and timely global view of emerging infectious disease threats. A truly open and accessible system can also assist users in overcoming existing geographical, organizational, and societal barriers to information, a process that can lead to greater empowerment, involvement, and democratization across the increasingly interconnected global health sphere.