ATLANTA – Four more people have been infected with Salmonella Heidelberg since June 2012, bringing the number of cases related to the outbreak to 128, according to Atlanta-based Centers for Disease Control. CDC said chicken is the most-likely source of infection for many of the affected persons. The outbreak has covered 13 states since the CDC last reported on it in February.

Thirty-two people have been hospitalized with the outbreak strain, according to CDC. Most of the illnesses are concentrated in Oregon (39) and Washington State (56). CDC said tests conducted by the Washington State Public Health Laboratories identified the outbreak strain in four intact samples of chicken collected from three sick persons’ homes in Washington. In February, Oregon and Washington had identified Foster Farms brand chicken as the most likely source of the infections in those states.

Foster Farms, Kelso, Wash., issued a statement in February emphasizing its commitment to safety and quality of its poultry products. The company did not issue a recall, saying "all raw chicken, like all raw meats must be responsibly handled and properly prepared to ensure safety and quality." The CDC also said it is not unusual for raw poultry from any producer to have Salmonella.

The USDA's Food Safety and Inspection Service is investigating the outbreak to determine the source of infections, CDC said.