Expert Report

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The proper inspection of meat and poultry products -- foods that are major contributors to human-foodborne illness -- is vital to the public health of our nation. The task belongs to the Food Safety and Inspection Service (FSIS) of the U.S. Department of Agriculture, which recently proposed a risk-based methodology for prioritizing its inspection of slaughtering and meat processing facilities. Facilities are ranked according to the risk their food products pose to human health, based (in part) on the proportion of illnesses attributable to those food products (such as deli meat and ground beef). At FSIS' request, this NRC letter report evaluates the agency's methodology for ranking facilities based on the extent to which their food products are potential sources of Salmonella, E. coli O157:H7, and Listeria monocytogenes infection. The report finds that allocating illnesses among food products is extraordinarily difficult because the assessment must cover the "farm-to-fork continuum" -- for example, a contaminant may pass from a bird to a chicken at the farm, from one chicken to another during processing, and from chicken to lettuce in a kitchen. Thus, an illness could be attributed to the lettuce, obscuring the importance of contamination in chickens much earlier in the continuum. The report recommends that FSIS consider using additional public health data and developing a methodology that more clearly presents the rationale behind the agency's approach. Further, because attribution data are scarce, FSIS should consider models for prioritizing risk that do not rely on food product attribution or that use attribution data in a different way.

Key Messages

  • Attribution estimates based on outbreak data which reflect disease occurring at the point of consumption do not directly translate to attribution at the point of slaughter and processing. Because the risk-ranking algorithm does not explicitly consider the contribution of non-regulated attribution sources to FSIS-regulated products, it can under or over-estimate the proportion of illnesses actually attributable to slaughter and processing.
  • Because FSIS estimates public-health effects on the basis of a small number of observations, the estimates have large uncertainties that should be communicated in the ranking algorithm.
  • Failure to characterize the uncertainty in the attribution estimates and other inputs of the risk-ranking algorithm is a critical weakness in the proposed PHRBIS.
  • In the proposed public-health risk-based ranking algorithm, FSIS's method of categorizing facilities on the basis of their LOI (indicators of process control) before incorporating public-health attribution (public-health effect) ranks facilities according to inspection-based risk (for example, recalls, enforcements, and verification testing). This ranking may not reflect public-health risk.
  • Salmonella serotyping and molecular subtyping not only will be critical for improved attribution efforts but will enhance the agency's ability to monitor pathogen trends, such as emergence of new subtypes. Salmonella serotype-based and subtype-based attribution models are not yet at a stage where they should be used for policy decision-making.
  • The data sources currently available for assessing attribution are insufficient to be used independently. FSIS has not used some data that are readily available to supplement the CDC outbreak data and expert elicitations.
  • The development of performance measures is premature, given the limitations of the attribution estimates and the lack of uncertainty characterization.
  • FSIS should also recognize that attribution estimates will need to be updated as disease incidence in humans changes to retain their relevance when used for risk-based inspection.
  • FSIS should present a more transparent algorithm to rank slaughtering and processing establishments according to public-health risk.