Two of the strains are resistant to two types and the agency said it was unsure what caused these strains to become resistant to antibiotics.
The outbreak has sickened 338 people from 20 states and Puerto Rico with 40% of ill people being hospitalized.
“Although health officials have not reported any deaths, the high hospitalization rate is twice the norm. An unusually high rate of blood infections (about 14%) requiring treatment with antibiotics has been reported in this outbreak,” said the CDC.
Foster Farms identified
Foster Farms chicken has been named as the likely source of the Salmonella Heidelberg illnesses.
However, there has been no recall as USDA-FSIS said products are safe to eat as long as they are properly handled and fully cooked to an internal temperature of 165°F.
Most of the ill people (75%) have been reported from California and among 331 people for which information is available, illness dates range from 1 March to 2 October, ages from less than 1 year to 93 years, with a median age of 18 years.
Dr Chris Braden, head of CDC’s division of foodborne, waterborne, and environmental diseases and an infectious disease specialist, said: “In general, antibiotic use in food animals can result in resistant Salmonella, and people get sick when they eat foods contaminated with Salmonella."
Ongoing story
Mexico has banned imports of Foster Farms chicken from three plants implicated in a Salmonella outbreak.
USDA officials said this is the first time Mexico has delisted a facility based on a public health alert by the agency's Food Safety and Inspection Service.
CDC reported on another outbreak of Salmonella linked to Foster Farms chicken which sickened 134 people in July this year.
Ron Foster, President of Foster Farms, said the firm had made progress to break the chain of Salmonella from the ranch to the store.
“Since October 11, Foster Farms has introduced 23 new Salmonella-control measures. We have drawn upon the best advice, the best technology and the best efforts of our employees to develop these new programs, which have proven effective.”
Meanwhile, the USDA-FSIS quarterly progress report on Salmonella and Campylobacter testing showed Salmonella on raw young chicken carcasses was down 34% over Q1 2013, said the National Chicken Council.
The report contained testing from 1 April to 30 June and looked at selected raw meat and poultry products.
For young chicken carcasses, 2,955 samples were collected and analyzed with a positive rate of 2.6% for Salmonella – compared to the USDA FSIS performance standard of 7.5%.