There may have been an early signal of the Listeria outbreak on the Internet long before the outbreak went public, finds an intriguing new report published in the Canadian Medical Association Journal.

The report is an analysis of Internet-based surveillance of last summer's Listeriosis outbreak that was linked to tainted meat from Maple Leaf Foods. The report finds that while the Canadian public was informed by federal officials on Aug. 20, 2008, of the nationwide outbreak, Internet searches for the word "listeriosis" spiked in mid to late July -- almost a month before the announcement.

Interestingly, peak searching for "listeriosis" correlated with a spike in the number of illness cases, which were later confirmed retrospectively.

There was also a big increase in searching for the word "Listeria" that exactly coincided with the announcement and the ensuing news media attention.

"Therefore, it appears that there was a clear Internet signal related to "Listeria" that preceded the official federal announcement," conclude the authors, 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.

By the time the outbreak was announced, only one person had died and 16 cases of listeriosis had been identified. Another 19 deaths and hundreds more cases of illness have since been linked to the outbreak, which triggered the largest meat recall in Canadian history.

Why the term "listeriosis" was searched more than "Listeria" ahead of the announcement might be explained by the fact that listeriosis is more technical and may reflect Internet searches by food inspection or industry officials investigating the possibility of the outbreak.

The spike in searches could also be the result of queries by family and friends of people diagnosed early in the outbreak or by people concerned about the initial voluntary meat recalls, the CMAJ report authors suggest.

Public health officials have said they began to suspect a Listeria outbreak in mid-July 2008, when reports of illnesses began to grow. Ontario's health ministry was "actively investigating" cases in July, trying to connect the dots between patients but the meat recall was delayed for weeks while samples were tested at a Health Canada lab in Ottawa.

"A question that arises from this analysis is whether knowledge of this information, either by public health officials or members of the public, could have prompted an earlier response that may have reduced exposure to the contaminated products," the report authors write.

The Internet is revolutionizing infectious disease surveillance, providing a timely and low-cost resource for public health officials to detect disease outbreaks.

Google Flu Trends, for example, now provides both public health professionals and the general population with a real-time geographically specific view of influenza search activity in the United States.

Public health officials also use tools such as the Global Public Health Intelligence Network, developed by Health Canada, and Program for Monitoring Emerging Diseases. They also use HealthMap, a free, real-time system that maps reports on emerging diseases across the globe.

And the World Health Organization has long relied on Web-based data sources for daily disease surveillance.

"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," the authors write.

The authors caution, though, that there are limitations to online tools, such as false alarms and risk communication problems for public health officials. What's more the potential for the tools is limited in developing countries and areas that have a lack of Internet access.

"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."

Health authorities began to suspect in mid-July that more than coincidence lay behind two people from the same Toronto nursing home who developed a dangerous bacterial infection, officials said Friday.