Despite modest improvement in some numbers, our findings suggest that most companies' safeguards might be inadequate. To tease out what might account for Perdue's and Bell & Evans' relative success, we asked those companies as well as Tyson and Foster Farms whether they have added any food-safety measures in the past few years. We didn't reveal our test results.

Bruce Stewart-Brown, Perdue's vice president of food safety and quality, and a doctor of veterinary medicine, told us the company has increased its salmonella vaccinations over the past few years. That's designed to prevent chicks from picking up the bacterium from their mothers. Further protections, Stewart-Brown said, include an "all-in, all-out production model." Translation: Flocks are cleared out completely. Between flocks, farmers dry the empty chicken houses (which kills bacteria) and often use a product that temporarily changes the pH of the ground (to make it inhospitable to bacterial growth). Birds on each farm are the same age, so there are no older birds to contaminate newly arrived younger ones. "We also work closely with the farmers that raise our poultry," he said. "We make sure they isolate any other species of animals that might transfer microbiology to our chickens, use footwear and clothing control programs, and closely regulate visitation by outsiders."

Stewart-Brown also says that Perdue has implemented 25 food-safety steps at its processing plants.

Tom Stone, director of marketing at Bell & Evans, which produced those clean chickens, said the company has started packaging its products with a machine that seals the edges with film and shrinks the material, so there's no need for a "diaper" under the chicken to sop up fluids. "Our chickens are air-chilled and carry the ‘No Retained Water' statement," he said.

But listen to Foster Farms and Tyson and you'd think they would have been as clean. Robert O'Connor, vice president of technical services at Foster Farms and a doctor of veterinary medicine, cited the company's use of "the most technologically advanced and proven systems available." Tyson spokesman Gary Mickelson said his company's safeguards include keeping hatcheries sanitized, vaccinating some breeder stock against salmonella, and ensuring proper refrigeration during product delivery.

Our own experts say that controlling the spread of bacteria is a matter of being vigilant and taking many small steps, from hatchery to store, rather than relying on one magic bullet. A May 2008 release of USDA compliance guidelines for the poultry industry recommends 37 "best practices," including controlling litter moisture in chicken houses and continuously rinsing carcasses and equipment in processing plants. Chicken producers that follow good practices in the hatchery and on the farm and abide by those government guidelines should be able to produce fewer chickens that harbor salmonella, though not necessarily campylobacter.