NFPA collected and tested about 31,700 samples in eight different categories of ready to eat foods. Samples were collected and tested over a period of 14-23 months from retail markets in Maryland and California Food Net sites. The product categories on the access database include fresh soft "Hispanic" style cheeses, bagged salads, blue veined and soft mold ripened cheeses, smoked seafood and seafood salad. The access database includes information on the product, such as location packaged, geographic area, date listed, date of purchase, date of assay, if vacuum packaged, etc. Test information also includes presumptive positives, number of tubes that are turbid at the 1, 10 and 100 dilution, most probable number, presumptive colonies, cfu/g, etc.

Survey results were published in: 
Gombas D.E., Chen Y., Clavero R.S., Scott V.N. Survey of Listeria monocytogenes in Ready-to-Eat Foods, Journal of Food Protection: Vol. 66, No. 4, pp. 559-569. April, 2003