People are eager to talk, says D-team member Jena Trask, who has been with the group for more than two years and graduated in spring with a master of public health degree in epidemiology. "They tell us more about their symptoms than they would anyone in their own family." In half-hour interviews, the team also asks what grocery stores, restaurants or large gatherings the person has visited and about exposure to farm animals. The interviewer gathers a food history starting from five days before the onset of poisoning symptoms. "Without the interviews," Trask says, "we would catch a very small percentage of these outbreaks."

The excitement starts when patterns begin to emerge and the team begins to form and test hypotheses about the source of the pathogen, as with an E. coli outbreak this summer. "You usually find E. coli in ground beef or prepackaged lettuce," Trask says, but that didn't hold true in these cases. One clue: a high number of young females and children were sick. After narrowing down the possibilities, it became increasingly clear that the culprit was raw cookie dough.

Team D uses a dynamic cluster investigation model, which means that as they zeroed in on the dough, they continually refined the questions they asked incoming cases and systematically reinterviewed the first cases to assess whether these sickened victims were exposed to E. coli via cookie dough. In some investigations the team assembles and interviews a control group, which allows them to do a statistical comparison between, for example, those who ate cookie dough and were sickened and those who were not. As it turned out, the team was dealing with an outbreak that sickened 80 people from 31 states. The dough was traced to specific batches from Nestlé USA, and the company subsequently recalled 3.6 million packages of cookie dough. How the contamination occurred remains a mystery.

Such outbreaks expose the weaknesses in the country's overall reporting system because some states have no one to conduct interviews and many use a decentralized group of counties and municipalities to collect information, often when it is too late to get good data. And, according to Ian Williams, chief of the CDC's OutbreakNet, which collaborates with a national network of epidemiologists to investigate outbreaks of intestinal diseases, the problem of food contamination is growing. "In the last 10 years food distribution has changed dramatically both in speed and in the distance that food is transported," he says. "There are more industrial contamination events every day."

All this talk of food-borne illness is enough to make an investigator lose her appetite, says Team D member Carrie Klumb, also a recent recipient of a master of public health degree who is beginning a CDC/CSTE (Council for State and Territorial Epidemiologists) applied epidemiology fellowship with the MHD specializing in zoonotic diseases (infectious diseases that can be transmitted between humans and other animals, such as "mad cow" disease and West Nile virus). "I had a period where I felt like I couldn't eat anything," she says. "But you can be smart about the risks you take—no steak tartar, for example."

Ultimately, avoiding food poisoning may be a matter of luck. "I ate some of the raw cookie dough that caused the outbreak," Klumb says, "but I didn't get sick. It's amazing how often we don't get sick."

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