After 9/11/01, the CDC Division of Public Health Surveillance with help from Homeland Security implemented a new program for tracking possible bioterrorist threats, known as syndromic surveillance. Instead of relying on medical diagnosis of individual doctors, the system looks for statistical anomalies across the symptoms reported in recent emergency room visits and notifies epidemiologists when attention is needed. Doctors tend to use the Occam’s Razor approach to diagnosis, assuming that common illnesses are the cause for most medical visits; without any awareness of hospital- or city-wide statistics, a bioterrorist assault could go undetected for weeks until initial cases had progressed into more severe symptoms.
This approach to surveillance strikes me as ultra-futuristic, allowing machine intelligence to process large amounts of data that no individual doctor could take into perspective. While the system is developed (and funded) for the purpose of thwarting bioterrorist attacks, it’s easy to imagine a number of other uses for syndromic surveillance: seasonal viruses, STDs, macroparasites, and so on. Given an appropriate sensitivity, it could even be used to replace Erin Brockovich, finding carcinogenic sites based on a few reported cases and an abnormality in symptoms. Of course there will be a number of unexpected uses as well.
New York City has had a syndromic surveillance system in place since shortly after 9/11, and Epidemic Intelligence Service (EIS) officers have been monitoring this data ever since. One of the first real alarms set off by the system came shortly after the power outage in August of this year when emergency rooms were flooded with reports of diarrheal illness. This symptom was far out of the range of others being reported, and suggested a possible power-related outbreak of some microbial agent probably linked to either the food or water supply. NYC health officials issued a health advisory warning people to make sure food that had lost refrigeration was properly disposed of. Thankfully, within a few days the consistency of bowel movements returned to normal, and the city resumed its life.
So who said the Department of Homeland Security was all bad? It’s interesting that a system meant to thwart bioterrorism has never detected such an act, but goes off every time the city eats too much McDonalds. Here we were looking for the black plague and we found the brown one instead… and saved a lot of people from extended dietary discomfort.
CDC DPHST: Syndromic surveillance
NYC Department of Health: Citywide increase in diahrreal illness
overstated 
syndromic surveillance is a perfect example of Einstein’s Razor – theories should be as simple as possible, but no simpler. The only thing syndromic surveillance has detected to date are outbreaks that were perfectly predictable in advance.