Which is to say that the power of the Internet to amass ever-larger haystacks of information makes it more and more difficult to find the needles. According to Associate Editor Marjorie Pollack, M.D., ProMED’s lead moderator during the SARS outbreak, “Do you post every individual unknown case of everything? What’s your threshold? What will your system tolerate? Is a single undiagnosed case of something unusual of global importance?”

Yet a mass of data culled from news aggregators is riddled with false positives and false negatives. “We deal with a spectrum of electronic information. It’s a constant tradeoff between sensitivity and specificity,” says John Brownstein, Ph.D., an assistant professor of pediatrics at Harvard University Medical School.

Brownstein has fashioned a different form of electronic surveillance: real-time disease mapping. With computer scientist Clark Freifeld, he is scraping news aggregators such as Google News, as well as ProMED, WHO reports, and other sources, using software that matches a glossary of infectious disease terms with words related to geography. He then superimposes his results against a background of gorgeous Google satellite maps.

Brownstein’s HealthMap is the first real-time disease alert that conveys facts graphically rather than verbally—a comprehensive and dynamic portrait of the world’s well-being. Viewers can scan cities, countries, or continents for hourly updated reports. Teardrop-shaped “heat” markers indicate the level of urgency: red for, say, ongoing outbreaks of Ebola in Uganda or human “bird flu” cases in Egypt, yellow for older reports of food recalls, and the like. Viewers can click on news updates, and cut the data according to news feed, disease, country, or timeliness.

Brownstein’s quest to deep-mine the Internet sprang from the realization that just about everything a disease cartographer needs is already on the web. “We use tools that are freely available and data sets that are open to the public,” he says.

 Who clicks on HealthMap? Not only web surfers, but also governments and public health officials. In a world where pathogens need no passports, bureaucrats often don’t know what’s fulminating just across the border—and could soon jump into their own backyard. Brownstein’s next ambition is to track increases in keyword searches by geographic region. With algorithms linking Google Trends—which displays the top cities, regions, and languages in which users type in a given search term—to Google Maps, he hopes to lexically locate nascent emergencies. Such an approach may have uncovered, for instance, a surge in searches for “pneumonia” and “flu” in Guangdong in late 2002.

The Internet’s most salutary effect on public health is that governments can no longer hide outbreaks—though, as SARS proved, they can try. Ever since the WHO passed its revised International Health Regulations in 2005—an agreement to contain emergencies at the source, not only at national borders—the agency has relied more and more on “informal sector reports” from media and websites, and less on official candor. Before these new regulations, the WHO itself used to publish a weekly Outbreak Verification List, known in the trade as the Wednesday “rumor list,” a tally of unconfirmed disease reports from all over the world that only a select group was permitted to read. Now the Internet generates its own rumor lists—24/7, for anyone to peruse.

A GPHIN or ProMED posting is a wedge for the WHO to convince reticent nations to come clean with the truth—or for outside authorities to investigate. As GPHIN chief Abla Mawudeku puts it, “WHO can knock on a country’s door and say, ‘We have some information about an event occurring in your backyard. It’s from the media. Could you help verify this?’”

As communications technology gains definition, so will disease surveillance. “We can locate outbreaks within countries and provinces, but we can’t locate them within a farm or village,” says Madoff. “In a blue sky future, I can envision being able to know where individual cases are.”