No one died, although one person went to the emergency room with heart trouble in the incident, which occurred at a Family Fare store in Grand Rapids, Mich., at the turn of the year.

A report on the incident appears in Friday's Morbidity and Mortality Weekly Report, issued by the U.S. Centers for Disease Control and Prevention.

Federal authorities have charged Randy Jay Bertram with deliberately poisoning the meat, according to WOOD, a Grand Rapids television station. Bertram was described as a "disgruntled employee" seeking revenge on the market, according to the station.

Officials say Bertram used a substance called Black Leaf 40, a pesticide with a high concentration of nicotine. The substance was banned in the United States in the early 1990s because of its toxicity.

Dr. Matthew Boulton, Michigan's state epidemiologist, says the case underscores the difficulties health officials face in policing the nation's food supply at the retail level.

"Surveillance systems can certainly alert us to infectious contaminations and then we can rapidly intervene. But in a situation like this, it would have been difficult for public health [workers] to have done anything different. It's very difficult for us to control malicious acts," says Boulton, co-author of Thursday's CDC report.

The Sept. 11, 2001, terror attacks and the anthrax mailings a month later sent food safety officials scrambling to bolster the security of the country's food supply.

Steven Cohen, a spokesman for the U.S. Department of Agriculture's Food Safety and Inspection Service, says the agency has "stepped up our monitoring program considerably" since 9/11. Inspectors now screen meat and poultry products for "things you wouldn't expect to find" in them, though Cohen declined to name these harmful agents.

The USDA does have the authority to test products on supermarket shelves, Cohen adds. However, the agency believes its actions accomplish the most good at the production level.

This week, the Food and Drug Administration (FDA) proposed two new regulations it believes will further protect the food supply from a terrorist threat.

One of the rules would require food manufacturers, processors, packers, distributors, receivers, holders and importers to keep records of where their products come from and where they're sent. These records would serve as a paper trail of a food item's provenance and let inspectors track who had control of it and when.

The second rule would give the FDA greater authority to detain suspect food items. The policy does not cover foods under the USDA's purview, which include meat, poultry and egg products.

Carl Winter, director of the FoodSafe program at the University of California, Davis, says Americans enjoyed relatively safe food even before the actions inspired by September 11. "I feel we're in the same position now," he says.

Winter believes food processors have made strides in safeguarding their plants, steps that could protect consumers against intentional attacks. But "as long as people are involved in our system, there is the potential for errors or gross malice. I think that's going to be something we'll just have to live with."

Fortunately, experts say, incidents of malicious large-scale tampering with the food supply are rare. The CDC report cites only two previous cases, including a salad bar in Oregon tainted with salmonella.