Estimating correlation of prevalence at two locations in the farm-to-table continuum using qualitative test data.
To evaluate whether the number of Escherichia coli bacteria in carcass rinses from chicken slaughter establishments could be monitored for the purpose of microbial process control, we drew a random sample from 20 of 127 large USDA-inspected operations. In 2005, every 3 months, two sets of 10 carcass rinses, 100 ml each, were collected from establishments, netting 80 sample sets from the rehang and postchill stages. E. coli and Campylobacter numbers and Salmonella prevalence were measured. Mixed-effect models were used to estimate variance of mean log(10) E. coli cell numbers of 10-carcass rinse sample sets. Relationships between E. coli and Campylobacter and Salmonella were examined. For 10-carcass rinse sets, at both the rehang and postchill stages the mean log(10) E. coli CFU/ml fit the logistic distribution better than the normal distribution. The rehang overall mean log(10) E. coli was 3.3 CFU/ml, with a within-sample set standard deviation of 0.6 CFU/ml. The overall postchill mean log(10) E. coli was 0.8 CFU/ml, with 13 establishments having mean log(10) E. coli CFU/ml values of less than 1.0 and 7 having mean values of 1.2 or more. At the midpoint separating these establishments, a mean log(10) E. coli CFU/ml of 1.1, the within-sample set standard deviation was 0.5 CFU/ml, with smaller standard deviations as means increased. Postchill sample sets with mean log(10) E. coli counts less than or equal to 1.1 CFU/ml had lower overall prevalence of Salmonella and mean log(10) Campylobacter CFU/ml than sample sets with higher means. These findings regarding reductions in E. coli numbers provide insight relevant to microbial process control.