Catherine Strommen, an elementary school teacher in Fremont, California, padded to the kitchen computer and took one last look at her favorite chat room, Teachers.Net. It was midnight, February 9, 2003. At that late hour, two or three stray chatters were scrolling down the screen—likely Asians or Australians, who usually logged on when Americans were turning in.  

One of the posts came from China—someone who called himself “Ben” (most adopted Anglo names). But his tone was distinctly different from the usual exchanges about pedagogy, food, and literature. In tenuous English, he described an illness that started like a cold, but killed its victims in days. A friend who worked in a hospital had died, as had the friend’s mother. In Guangdong Province, where Ben resided, hospital doors were locked.

Alarmed, Strommen emailed an old neighbor and friend, Stephen Cunnion, M.D., a retired Navy physician and epidemiologist who now lived in Maryland. A practical, no-nonsense man, Cunnion started searching the web. With no success, he tried a new tack—sending an email to ProMED-mail, a global electronic reporting system for outbreaks of emerging infections and toxins. After quoting Strommen’s missive, he asked: “Does anyone know anything about this problem?”

The tiny ProMED staff conducted its own web search. It, too, came up empty-handed. On February 10, it sent out to tens of thousands of subscribers a posting headed: “PNEUMONIA – CHINA (GUANGDONG): RFI,” or Request for Information.

Thus did the world first learn of SARS, the new and deadly infection that would kill 774 people and infect 8,000 in 27 countries. The next day, the World Health Organization issued a belated bulletin on the raging epidemic.  

Welcome to modern disease surveillance. When a serendipitous exchange on a teacher’s chat room morphs into a global outbreak alert, public health practice will never be the same. Until a few years ago, we had to wait for bureaucrats to announce disease emergencies within their borders. Today, abetted by the Internet, outbreak news is highly contagious. Web crawlers, automated translation, GIS mapmaking, ISP tracking, and cell phone imagery have created a world where, for good or ill, rumors of outbreaks outpace confirmation.

And it’s not just fast-moving infections that are flushed out by high technology. Social epidemics, such as the next new fad in drug abuse, are also being monitored through canny—and perfectly legal—eavesdropping on public electronic forums. The Internet has even been used to intervene in public health emergencies—by emailing, for example, online daters exposed to sexually transmitted diseases.     

If Hippocrates were alive today, he’d probably write a treatise on the Internet. But even in his time, he had a plugged-in perspective. In the classic On Airs, Waters, and Places, he described in vivid detail how disease was influenced by the seasons, winds, water, geography, and what today we would call “lifestyle.” Armed with those facts, aspiring healers, he wrote, “must proceed to investigate everything else.” In 2008, that’s just what’s happening online. The father of medicine would probably need three laptops to keep up with it all.