ATLANTA – An outbreak of Salmonella Heidelberg linked to Livingston, Calif.-based Foster Farms chicken products has sickened more people, prompting the Centers for Disease Control and Prevention in Atlanta to reverse its earlier stance that the outbreak appeared to be ending.

CDC announced that as of Jan. 15, a total of 430 people were infected with seven outbreak strains of Salmonella Heidelberg. But the latest information from the agency indicates that, as of Feb. 28, a total of 481 people were infected. Illnesses have been reported from 25 states and Puerto Rico, since March 1, CDC reported.

Salmonella Heidelberg outbreak timeline. Click to enlarge

"The number of reported infections from all seven outbreak strains of Salmonella Heidelberg returned to baseline levels in January and the outbreak appeared to be over, as noted in the previous update on January 16, 2014," CDC said on its website. "However, the investigation continued and ongoing surveillance in February identified that infections from two of the previously rare outbreak strains have again exceeded the number of infections expected to be reported to PulseNet during this time of year."

Since the last update on Jan. 16, 51 new infections have been reported from Arizona (3), California (44), Hawaii (1), Tennessee (1) and Utah (2), according to CDC.

The agency added that the outbreak strains have shown resistance to several commonly prescribed antibiotics, although those antibiotics are not typically used to treat Salmonella infections or other severe Salmonella infections.

Under threat of plant closures by the US Department of Agriculture's Food Safety and Inspection Service, Foster Farms implemented a number of food-safety interventions at three of its California processing plants that were linked to the outbreak. No recall notice was issued in the case, but some stores pulled Foster Farms products from shelves. Foster Farms suffered another setback when the company temporarily closed its Livingston poultry plant after the discovery of cockroaches at that facility. The company re-opened the plant on Jan. 22.