The Internet is revolutionizing infectious disease surveillance, providing timely, low-cost online resources for public health officials to detect disease outbreaks. An analysis in CMAJ of web-based disease surveillance of the recent Listeriosis outbreak in Canada demonstrates there may have been an early signal of the outbreak on the Internet prior to the official announcement click here for further information.

Rapidly identifying an infectious disease outbreak is crucial to reduce the spread of disease and to alert the public and neighbouring regions. Information sources, such as chat rooms, search terms, blogs, news feeds and other real-time sources are often capable of detecting the first evidence of outbreaks.

Many countries lack the public health infrastructure to identify outbreaks in the early stages and there may be economic reasons for countries to not fully disclose infectious outbreaks. Online tools can help overcome some of these obstacles.

"Because web-based data sources exist outside traditional reporting channels, they are invaluable to public health agencies that depend on timely information flow across national and sub-national borders," write Dr. Kumanan Wilson, Ottawa Health Research Institute and Department of Medicine, University of Ottawa, and Dr. John Brownstein of Children's Hospital Boston and Harvard Medical School.

The World Health Organization relies on web-based data sources for daily disease surveillance. Tools such as the Global Public Health Intelligence Network, developed by Health Canada, and Program for Monitoring Emerging Diseases are used by public health officials. HealthMap (http://www.healthmap.org) is a free, real-time system that maps reports on emerging diseases across the globe. Applications such as Google Flu Trends, which examine trends in search terms that correlate with disease, represent an emerging new area of surveillance.

Applying this form of online surveillance to the Listeriosis outbreak in Canada in summer 2008 provides some interesting findings. While HealthMap collected 89 original articles about the outbreak beginning August 17, 2008, search terms using the word "listeriosis" spiked in mid-late July, almost a month before the outbreak was publicly declared.

"Interestingly, peak searching for "listeriosis" correlated more with the retrospective epidemic curve than with the publicity of the outbreak as measured by news volume," write the authors.

While online tools can be useful there are limitations, such as signal overload, false indicators of an outbreak, risk communication problems for public health officials and lack of Internet access in developing countries.

"Internet scanning represents an important advancement in health surveillance and search term surveillance is a provocative new tool that has much potential but both merit further evaluation," conclude the authors. "Most importantly, these technologies may provide significant benefits to outbreak control at local, national and international levels, ultimately reducing the health consequences of these outbreaks."

CMAJ - Canadian Medical Association Journal