Microbiological Surveillance Sampling: FY14-16 Raw Milk Cheese Aged 60 Days
In 2014, the U.S. Food and Drug Administration (FDA) set out to collect and test cheese made from unpasteurized milk, also referred to as “raw milk cheese,” aged 60 days as part of a new proactive and preventive approach to sampling with the ultimate goal of keeping contaminated food from reaching consumers.
The new approach, detailed in the report available below, centers on the testing of a statistically determined number of samples of targeted foods over a relatively short period of time, 12 to18 months, to ensure a statistically valid amount of data is available for decision making. This approach helps the agency determine if there are common factors – such as origin, variety or manufacturing practice – associated with any pathogen findings.
The FDA issued the raw milk cheese assignment in January 2014 along with two others (for sprouts and avocados) as the initial commodities under its new sampling model. As planned, the FDA collected 1,606 raw milk cheese samples (exceeding its target by 6 samples). The FDA designed its sampling plan such that if contamination of one percent or greater was present in the commodity, the agency would detect it. The agency closely monitored the assignment to gather lessons learned and make changes to the sampling if needed to address trends or food safety issues.
Of the 1,606 raw milk cheese samples collected and tested, 473 samples (29 percent) were domestic samples, and 1,133 samples (71 percent) were of international origin. The FDA sought to design its sampling plan to approximate the ratio of domestically made versus imported product on the U.S. market but was unable to do so in this case because the federal government does not track production volume of raw milk cheese. Details on the assignment design are provided in the Sample Collection section of the summary report.
The FDA tested samples for the presence of the pathogens Salmonella, Listeria monocytogenes, E. coli O157:H7 and Shiga toxin-producing E. coli, as well as for generic E. coli. The overall contamination rate for each of the pathogens was less than one percent, and the overall contamination rate for generic E. coli was 5.4 percent. While the prevalence for generic E. coli was comparatively high, it bears mention that it rarely causes illness even as it may signal insanitary processing conditions.
Because the contamination frequencies among the pathogens were below one percent, the FDA was limited in its ability to detect differences in contamination rates based on the type of cheese or its origins (i.e., domestic vs. import), even with the large number of samples.
In addressing the violative samples of domestic raw milk cheese, the FDA worked with the responsible firms to carry out recalls as appropriate and followed up with facility inspections. In addressing the violative samples of imported raw milk cheese, the FDA refused entries of raw milk cheese and placed the responsible firms/product on Import Alert 12-10. The FDA also worked with a regulatory partner in the European Union to address further follow-up of manufacturing locations abroad.
Listeria monocytogenes in cheeses, particularly semi-soft varieties, remains a concern, as demonstrated by the nearly one percent contamination rate in semi-soft cheeses (see report Appendix B: Positive Findings by Bacterial Type). The FDA believes this contamination rate may be related to product handling practices or procedures. Given the serious public health implications of Listeria monocytogenes contamination associated with ready-to-eat foods, the FDA plans to continue to work with the cheese industry to identify and correct practices that lead to Listeria monocytogenes contamination in cheese.
1. The USDA Economic Research Service tracks the supply and commercial use of cheese in the United States but has no figures specific to raw milk cheese, which differs mainly with respect to the lack of pasteurization even as it comes in many varieties.