Cases of food-borne illnesses, including infections such as salmonella and Escherichia coli that have been at the center of recent outbreaks, have held steady for the past four years, federal health officials said today.

Salmonella was the most common bacteria transmitted by contaminated food last year, according to today's Morbidity and Mortality Weekly Report (MMWR). Rates of the infection, which has sickened 691 people and possibly killed nine in a recent outbreak via tainted peanut butter, have decreased the least of the nine illnesses that the U.S. Centers for Disease Control and Prevention (CDC) documents in the report.

The results are based on diagnoses of bacterial or parasitic illnesses from sites in 10 states, part of the CDC's Foodborne Diseases Active Surveillance Network (FoodNet), which began in 1996. Among the 18,499 infections recorded by FoodNet last year, 7,444 were salmonella, for a rate of 16.2 cases per 100,000 people. The other infections FoodNet tracked were Campylobacter, Cryptosporidium, Cyclospora, Listeria, E. coli O157,  Shigella, Vibrio and Yersinia. All can cause diarrhea, cramping and fever. They were most common in kids younger than four and deadliest in people 50 and older.

Exactly why rates of food-borne illnesses have flattened isn’t entirely clear, Robert Tauxe, deputy director of the CDC's Division of Foodborne, Bacterial and Mycotic Diseases, said during a teleconference call today.  Rates declined from 1996 to 2004; the fact that they've leveled out since then reflects weaknesses in the U.S. food-safety system, Tauxe said.

More fresh produce has become tainted in the past decade than in years before, Tauxe said. In addition, increasing links in the food-supply chain (whether farms, manufacturers, processors, distributors or retailers) provide more opportunities for contamination, Stephen Sundlof, director of the U.S. Food and Drug Administration's (FDA) Center for Food Safety and Applied Nutrition, said during the teleconference. 

"Our pathogens have complicated ecologies and may be changing," Tauxe said. "Our food industry is a complicated and changing arena, with different components and suppliers from all over the world. It's complicated and continuing and something I'm optimistic with coordinated efforts can be controlled in the future."

The salmonella outbreak (traced to peanut butter and paste from the Peanut Corporation of America) and other, recent high-profile outbreaks of that disease in jalapeno peppers as well as E. coli in beef and spinach, prompted President Obama in February to call for a review of  U.S. food safety practices. In recent weeks, pistachios and products containing them were recalled and the FDA warned consumers not to eat them after batches of the nuts were discovered to be contaminated. .

The agency also has hired 150 more inspectors, 32 additional scientists and safety officers and has distributed grants to six states (Florida, California, North Carolina, Minnesota, Michigan and Massachusetts) to set up "rapid response" teams that could check out local outbreaks of food-borne infections. "This plateau has to be addressed with a proactive, dynamic approach to protect American consumers," David Acheson, the FDA's associate commissioner for foods, said during the teleconference.

Low-temperature electron micrograph of E. coli/Eric Erbe and Christopher Pooley, USDA via Wikimedia Commons