An integrated approach to improve surveillance for foodborne pathogens of animal origin

Background: Foodborne pathogens are associated with an estimated 48 million illnesses, 128,000 hospitalizations, and 3,000 deaths annually in the United States. Annual cost of these illnesses is enormous (~ $158 billion).  Despite progress in molecular lab methods, electronic information systems and increased plant inspections, pathogens of animal origin (e.g., Salmonella) remain a leading cause of foodborne illnesses. Limited data on potential sources hinders prevention efforts and outbreak investigations. To address this gap, Pennsylvania has taken an integrated approach that compares data from retail food and clinical sources.

Methods: During August 2009 through April 2012, we tested for Salmonella in 650 samples of chicken breasts and ground turkey (325 each) purchased from randomly selected retail outlets in Southeast Pennsylvania. Salmonella isolates were analyzed by pulsed-field gel electrophoresis (PFGE) and compared manually to clinical isolates in the Pennsylvania database.

Results: Fifty one (15.7%) of the chicken samples and 33 (10.2%) of the turkey samples were positive for Salmonella.  Of the 83 isolates available for analysis, 44 (53%) had unique XbaI patterns while 39 (47%) were recurring. Using manual comparison, eight different PFGE subtypes (i.e., two-enzyme pattern combinations) were found in both retail food samples and ill patients during the 33-month period of the study.  Four of these matches were from chicken samples and four were from turkey samples.  Four PFGE two-enzyme pattern combinations were observed in retail food within a time relevant to outbreak investigation.

Conclusion: Comparing Salmonella PFGE data from retail meat with that from human illnesses combined with prompt investigation can facilitate early recognition of local and national outbreaks. However, manual comparison is very time-consuming. Recently, a new automated method has been implemented in Pennsylvania to make these comparisons.  This is expected to streamline and improve the comparison process, allowing more prompt investigation and better trace back of contaminated food.