Quantitative microbial risk assessment (QMRA) development: QMRA for Staphylococcus aureus and Staphylococcus enterotoxin A in raw milk as an example

Concern regarding the safety of the world food supply has lead to increased interest in the development of methods and regulations to decrease foodborne illnesses and improve overall food safety. Quantitative microbial risk assessments (QMRAs) are powerful probabilistic modeling tools that can be developed to assist risk managers, public health officials, governmental agencies, and producers in identifying and quantifying the risk (probability of illness) associated with a particular food and food pathogen. Quantitative data are represented in QMRAs as probability distributions for parameters such as pathogen levels, storage temperatures and times, pathogen growth, toxin production, host susceptibility, dose-response relationships, and food consumption patterns. Random Monte Carlo sampling selects and records a value from each input probability distribution during each iteration of the QMRA model. Following thousands of iterations the level of risk associated with a certain food and pathogen is calculated. With sufficient data QMRAs can be developed to simulate all steps in the farm-to-fork continuum, simulate potential "what-if" or "worst-case" scenarios, and are extremely useful for evaluating and communicating the impact of preventative control measures and regulations.;A QMRA for Staphylococcus aureus and staphylococcal enterotoxin in raw milk was developed to determine the risk of intoxication from a serving of unpasteurized milk. This QMRA incorporated S. aureus concentration data collected by the UC Davis Dairy Food Safety Lab from 2,336 California dairies during 2005-2008 and U.S. milk consumption data from the NHANES 2003-2004 food survey. Three growth modules were developed to predict pathogen growth of S. aureus in raw milk following various production and storage conditions. All growth modules predicted the pathogen's concentration could surpass the 105 CFU/mL level of concern at the 99.9th or 99.99th percentile of milk servings and may represent a foodborne illness risk. A fourth module was developed to simulate the production of staphylococcal enterotoxin A (SEA). Results indicated SEA exposure at the 99.99th-percentile could potentially represent a dose capable of eliciting staphylococcal intoxication in all consumer age groups. This QMRA illustrates the utility of QMRA to address and identify potential food safety issues.