Rapid estimation of Salmonella enterica contamination level in ground beef - Application of the time-to-positivity method using a combination of molecular detection and direct plating.

Little progress has been made in decreasing the incidence rate of salmonellosis in the US over the past decade. Mitigating the contribution of contaminated raw meat to the salmonellosis incidence rate requires rapid methods for quantifying Salmonella, so that highly contaminated products can be removed before entering the food chain. Here we evaluated the use of Time-to-Positivity (TTP) as a rapid, semi-quantitative approach for estimating Salmonella contamination levels in ground beef. Growth rates of 14 Salmonella strains (inoculated at log 1 to -2 CFU/g) were characterized in lean ground beef mTSB enrichments and time-to-detection was determined using culture and molecular detection methods. Enrichments were sampled at five timepoints and results were used to construct a prediction model of estimated contamination level by TTP (superscript indicates time in hours) defined as TTP4: ≥5 CFU/g; TTP6: ≤5, ≥1 CFU/g; TTP8: ≤1, ≥0.01 CFU/g; with samples negative at 8 h estimated ≤0.01 CFU/g. Model performance measures showed high sensitivity (100%) and specificity (83% and 93% for two detection methods) for samples with a TTP4, with false negative rates of 0%.

Developing a risk management framework to improve public health outcomes by enumerating Salmonella in ground turkey.

Salmonella spp. continue to be a leading cause of foodborne morbidity worldwide. To assess the risk of foodborne disease, current national regulatory schemes focus on prevalence estimates of Salmonella and other pathogens. The role of pathogen quantification as a risk management measure and its impact on public health is not well understood. To address this information gap, a quantitative risk assessment model was developed to evaluate the impact of pathogen enumeration strategies on public health after consumption of contaminated ground turkey in the USA. Public health impact was evaluated by using several dose-response models for high- and low-virulent strains to account for potential under- or overestimation of human health impacts. The model predicted 2705-21 099 illnesses that would result in 93-727 reported cases of salmonellosis. Sensitivity analysis predicted cooking an unthawed product at home as the riskiest consumption scenario and microbial concentration the most influential input on the incidence of human illnesses. Model results indicated that removing ground turkey lots exceeding contamination levels of 1 MPN/g and 1 MPN in 25 g would decrease the median number of illnesses by 86-94% and 99%, respectively. For a single production lot, contamination levels higher than 1 MPN/g would be needed to result in a reported case to public health officials. At contamination levels of 10 MPN/g, there would be a 13% chance of detecting an outbreak, and at 100 MPN/g, the likelihood of detecting an outbreak increases to 41%. Based on these model prediction results, risk management strategies should incorporate pathogen enumeration. This would have a direct impact on illness incidence linking public health outcomes with measurable food safety objectives.

Quantitative Risk Assessment of Salmonella in Ground Beef Products and the Resulting Impact of Risk Mitigation Strategies on Public Health.

Salmonellosis incidence rates have not declined over the last 15 years in the US despite a significant Salmonella prevalence reduction in meat and poultry products. Ground beef is currently regulated using only qualitative Salmonella criteria, and Salmonella enumeration values have been proposed as an alternative for implementing risk-based mitigation strategies to prevent illnesses. The purpose of this study was to develop a quantitative microbial risk assessment (QMRA) model to estimate the annual number of salmonellosis cases attributable to the consumption of ground beef contaminated with Salmonella and investigate the impact of risk management strategies on public health. Model results estimated 8,980 (6,222-14,215, 90% CI) annual illnesses attributable to ground beef consumption in the US. The removal or diversion of highly contaminated ground beef production lots containing levels above 10 MPN/g (0.4%) and 1 MPN/g (2.4%) would result in a 13.6% (5,369-12,280, 90% CI) and 36.7% (3,939-8,990, 90% CI) reduction of annual salmonellosis illnesses, respectively. Frozen ground beef cooked at home was the consumption scenario of the highest risk for acquiring salmonellosis. Highly virulent serotypes accounted for 96.7% of annual illnesses despite only being present in 13.7% of ground beef samples. The removal of MDR Salmonella would result in decreased burden of disease with a 45% reduction in acute DALY annually. Focusing salmonellosis reduction efforts on removing highly contaminated ground beef lots, highly virulent Salmonella serotypes, and MDR Salmonella from not-ready-to-eat (NRTE) products were predicted to be effective risk prevention strategies.