The cockroach infestation that closed a Foster Farms chicken plant in Central California was the latest setback for the giant poultry company, which last year faced a salmonella outbreak that sickened more than 400 people.

The U.S. Department of Agriculture suspended operations Wednesday at a Foster Farms plant in Livingston, southeast of Modesto, and the 250,000-square-foot plant remained closed Thursday as the poultry giant tried to remedy the problem.

Several food safety experts said they were surprised that cockroaches prompted the USDA's Food Safety and Inspection Service to take action when it had failed to do so after last year's salmonella outbreak.

"We'd been urging them to do this for months and months," said Jean Halloran, director of food policy at Consumers Union, the advocacy arm of Consumer Reports magazine. "They should have shut it down as soon as the link was made to all these illnesses."

Wednesday's news couldn't have come at a worse time for the troubled company.

In October, Foster Farms President Ron Foster apologized for the salmonella contamination and vowed to work to significantly reduce the bacteria, which has been a problem for poultry producers throughout the country.

Foster Farms was hit by two outbreaks of salmonella, one in 2012 and one last year. In late October, Mexico, a top destination for U.S. poultry exports, blocked imports of chickens from Foster Farms plants in Fresno and Livingston because of salmonella concerns.

Despite intensifying demands for a recall, the USDA allowed the plants to remain open after the company developed new protocols to reduce the rates of contamination.

Foster said the company saw a 25% reduction in sales after the latest salmonella outbreak.

Now, in addition to health issues raised by the new infestation, consumers are confronted by the ick-factor of cockroaches meandering near their future dinners.

The USDA disclosed its decision in a strongly worded letter, which said inspectors found cockroaches at the facility five times since September, most recently on Wednesday. Inspectors spotted roaches this week at a hand-washing sink while "slaughter operations were in progress and exposed product was present on the kill floor," the USDA said.

"Pests are highly unsanitary given that they can come in contact with decomposing garbage or other organic materials," the USDA said in the letter, which was signed by Abdalla Amin, a deputy district manager in Alameda. "Cockroaches and other pests can transmit disease-causing pathogens, including bacteria."

Foster Farms released a statement that acknowledged the presence of cockroaches at the facility. The company said it completed a "sanitization and treatment" procedure and asked the USDA for permission to relaunch operations.

"A single incident is not acceptable, and we are committed to a zero tolerance policy," the company's statement said.

The USDA's decision doesn't affect two other Foster Farms processing plants, which continue to operate.

Glenn M. Young, a professor and food safety microbiologist at UC Davis, said the presence of cockroaches at a food-processing plant can be dangerous.

"Any kind of pest is an issue in a food-processing facility," Young said. "They can serve as a way of vectoring those organisms from one contaminating site to another. Salmonella commonly has a wide host range, which would include even cockroaches."

Bill Marler, a Seattle food safety attorney, said he doubts that the cockroaches found this week had anything to do with the salmonella outbreak. The dangerous bacteria is contained in chicken feces and is often spread during the slaughter and butchering of chickens.

This is why consumers are encouraged to fully cook chicken, a step that destroys bacteria.

"It will impact Foster Farms' bottom line more by grossing people out than it would sickening hundreds of people," Marler said. "I don't think it's a huge deal. It would be more problematic if it were cockroaches in a restaurant or a facility preparing ready-to-eat food."

The USDA said the suspension would remain in effect "until such time as you provide adequate written assurances of corrective and preventive measures to assure that meat and poultry products will be produced under sanitary conditions."

stuart.pfeifer@latimes.com