A simulation model for studying the role of pre-slaughter factors on the exposure of beef carcasses to human microbial hazards

A Monte Carlo simulation model was constructed for assessing the quantity o f microbial hazards deposited on cattle carcasses under different pre-slaug hter management regimens. The model permits comparison of industry-wide and abattoir-based mitigation strategies and is suitable for studying pathogen s such as Escherichia coli O157:H7 and Salmonella spp. Simulations are base d on a hierarchical model structure that mimics important aspects of the ca ttle population prior to slaughter. Stochastic inputs were included so that uncertainty about important input assumptions (such as prevalence of a hum an pathogen in the live cattle-population) would be reflected in model outp ut. Control options were built into the model to assess the benefit of havi ng prior knowledge of animal or herd-of-origin pathogen status (obtained fr om the use of a diagnostic test). Similarly, a facility was included for as sessing the benefit of re-ordering the slaughter sequence based on the exte nt of external faecal contamination. Model outputs were designed to evaluat e the performance of an abattoir in a 1-day period and included outcomes su ch as the proportion of carcasses contaminated with a pathogen, the daily m ean and selected percentiles of pathogen counts per carcass, and the positi on of the first infected animal in the slaughter run. A measure of the time rate of introduction of pathogen into the abattoir was provided by assessi ng the median, 5th percentile, and 95th percentile cumulative pathogen coun ts at 10 equidistant points within the slaughter run. Outputs can be graphi cally displayed as frequency distributions, probability densities, cumulati ve distributions or x-y plots. The model shows promise as an inexpensive me thod for evaluating pathogen control strategies such as those forming part of a Hazard Analysis and Critical Control Point (HACCP) system. (C) 1999 El sevier Science B.V. All rights reserved.