Use of a Poisson-Gamma regression model to assess the process hygiene criterion for Enterobacteriaceae on Irish sheep carcasses (original) (raw)

The new Poisson-gamma modelling framework for low b acterial counts has been used to characterise withi nbatch and between-batch variability in Enterobacteriaceae in pre-chill sheep carcasses using counts data from five abattoirs sampled on four different occas ion . The negative correlation between the mean and dispersion parameters of the within-batch true dist ribu ions (gamma) was accounted by a correlated ran omeffects model. Since no assumption of within-batch constant variance was followed, all probability estimations could be performed with confidence inte rvals arising from the variability in the within-ba tch spread given a certain within-batch mean. The model was used in the assessment of the actual performan ce of the process hygiene criterion set by EC 2073/2005, and estimated that only 0.93% (95% CI: 0-4.08%) of the batches of pre-chill sheep carcasses produced in Ir eland would be found to be above the m limit of 1.5 log CFU/cm (~88 CFU/cm) and no batches would be fou...