1. NFPA Survey on L. monocytogenes in Ready-to-Eat Foods Yuhuan Chen, Jenny Scott National Food Processors Association Research Foundation

2. 2 Publication: JFP 66(4) 2003 1.Survey of Listeria monocytogenes in Ready-to-Eat Foods David Gombas, Yuhuan Chen, Rocelle Clavero, Virginia Scott

3. 3 Initiation of Study Risk management decision –Funding from nine industry partners through NFPA –Seek strategy effective in reducing listeriosis Is there an alternative to “zero tolerance”? Seek more than one strategy to solve the problem “Listeria monocytogenes: low levels equal low risk” JFP 66(4) Yuhuan Chen, William Ross, Virginia Scott, David Gombas

4. 4 Project Objective Develop data relative to the risk of listeriosis to support science-based strategy for addressing L. monocytogenes in foods

5. 5 Study Design Product selection Number of samples Sampling site selection –Sampling location within FoodNet sites –Selection of retail stores within counties Other aspects –Handling of samples, testing lab selection, testing methods

6. 6 Product Selection Retail foods likely to contribute to consumer exposure –Products with relatively high prevalence –Products frequently consumed –Products not likely to be further treated

7. 7 Product Categories January 2000 – November 2001 Luncheon Meats (ham, bologna, poultry) Deli Salads (potato, tuna, pasta, cole slaw) October 2000 – November 2001 Bagged, Precut Leafy Vegetable Salads Blue-veined Cheeses Fresh Soft Cheeses Soft Mold-ripened Cheeses Seafood Salads Smoked Seafood

8. 8 Number of Samples Considerations –Prevalence thought to be low (< 5%) –Cost for enumeration high Assistance from FDA to estimate total number of samples needed

9. 9 Sampling Site Selection Areas where illness data are reliable –CDC active surveillance for listeriosis in FoodNet Sites –Case control study conducted Selected two FoodNet sites widely separated –northern California –Maryland

10. 10 Estimate of Total Number of Positive Samples n: total number of positive samples P: percent positive for the population d: desired upper bound on absolute error z: 1.96, 95% confidence level

11. 11 Estimate of Number of Samples Assume P=50% –Given value of percentage unknown –Conservative n=125, 250, 500; d=8.8, 6.2, 4.4% Total number of samples 2500, 5000, 10,000 –assuming 5% prevalence

12. 12 Total Number of Samples: Luncheon Meats and Deli Salads Initial plan –2500 samples per product per FoodNet site Two products: luncheon meats, deli salads Two sites: MD and CA –5000 samples per product –10000 samples total Actual collection doubled –Prevalence considerably lower than expected

13. 13 Sampling Locations in FoodNet Sites  Northern CA  Alameda and San Francisco counties (counties in the FoodNet site) Maryland  Five counties plus Baltimore City (FoodNet site)  Total 10 counties plus Baltimore City  All counties containing > 2% of population (listeriosis reporting statewide) Samples weighted by populations in county or city

14. 14 Sampling RTE Foods  In proportion to consumption  Luncheon meats and deli salads  Frequency of consumption within the geographical area based on CSFII  West for CA, South for MD  Example, luncheon meats ham-bologna- turkey/chicken  50%-30%-20% in MD  43%-30%-27% in CA

15. 15 Sampling RTE Foods  100 samples per week for luncheon meats or deli salads  75% from List A stores (major super markets)  25% from List B stores (other grocers)  25 samples per week for each of six categories  At least two List A and at least two List B stores  Supplementary lists of stores used as needed

16. 16 FOOD SAMPLE Enumeration Divide into Two Portions Screening Composite Negative, Stop Composite Positive, test individuals If positive, proceed to Enumeration * 9-tube MPN: 1.0-0.1-0.01 g MPN* (UVM-Fraser or BLEB) Direct plating (OXA or MOX) Confirmation L. monocytogenes isolate

17. 31,707 Samples Tested in 2000-2001

18. 18 Lessons from the Study Resource intensive –Three years/1.4 M –Industry support, government funding Team effort –Jenny Scott, David Gombas, et al. –Outside contractors for sample collection and analysis –Expert consultations Meetings with Agencies –Understand regulatory concerns –Seek feedback about study design and approaches

19. 19 Lessons from the Study Industry concerns to be addressed –Confidentiality issues –Issues with unfavorable regulatory attention Not identify ham, bologna, or chicken/turkey Samples collected by third party

20. 20 Lessons from the Study More information –Packaging location Store vs. manufacturer Did not design sampling accordingly to sale or consumption –Enumeration data An opportunity to leverage industry and government resources –Started study with two categories –Obtained funding from JIFSAN to collect data on six additional categories

21. 21 Acknowledgements Funding –Funding from industry partners through NFPA –USDA CSREES, FDA (JIFSAN) Technical assistance –Robert Blodgett –Jerome Schneidman –Wallace Garthright