As we bring in more food from all over the world, we also increase the risk of introducing less common infectious agents. Take, for example, the parasite Cyclospora, which is responsible for the recent contaminated salad mix. "Cyclospora is predominantly found in tropical and subtropical areas of the world," says Barbara Herwaldt, MD, a medical epidemiologist at the CDC. The organism first made a big splash in the U.S. 17 years ago, when it was linked to imported Guatemalan raspberries. Herwaldt says, "We still have a lot to learn about what causes it and how it spreads." This helps explain why the CDC and FDA have had difficulty stemming the outbreak that's now infected people in 24 states.

From Herwaldt's perspective, it's critical for people to see a doctor if their food poisoning symptoms last three days or longer. The more closely scientists can track potential pathogens, the better they can study them and prevent future outbreaks. As it is, researchers estimate that scientists have been able to identify the pathogens responsible for only a fifth of foodborne illnesses in the U.S.

Ironically, the biggest driver of improved food safety tends to be a food crisis. In 2006, for instance, when a strain of E. coli sickened more than 200 people and killed three after they consumed bagged baby spinach, food safety measures were overhauled. "Knowing we'd been operating at the best standard of quality before the outbreak, I realized we needed to rethink what we were considering the 'best,'? " says Will Daniels, head of the quality, food safety, and organic integrity program at Earthbound Farm, a facility associated with the outbreak. In response, the company created an extensive safety program that focuses on eradicating pathogens during every step of production. Other companies cleaned up their act too, and the rate of E. coli infections in the U.S. is now 10 percent lower than it was in 2006.

There's hope that we may be able to prevent outbreaks from other infectious pathogens: In July, the FDA proposed new rules in conjunction with the Food Safety Modernization Act (a landmark law passed in 2011—the first major update to food safety regulations in more than 70 years) to help stop unsafe food from making its way into the U.S. The FDA is now putting the onus on importers, requiring them to verify that their suppliers meet the same standards as domestic food manufacturers. "Most people consume produce and other foods every day and don't get sick," says Michael Taylor, the FDA's deputy commissioner for foods and veterinary medicine. "There's always going to be some risk of illness—it's impossible to have a pristine food supply—but we continue to make it safer all the time."

Next: How experts track an outbreak