Quantitative Microbial Risk Assessment of Staphylococcus aureus in Lettuce from Farm to Table

This study aimed to evaluate the risk of Staphylococcus aureus food poisoning associated with ready-to-eat lettuce for the purpose of providing theoretical references for adopting effective risk management measures.

The incidence and level of S. aureus contamination in environmental samples from lettuce planting in greenhouses or open fields were investigated. With regard to hazard recognition, the description of hazard and risk characteristics and exposure estimation, a risk assessment of S. aureus food positioning caused by eating raw lettuce in China was carried out based on residents’ consumption habit survey data from the statistical yearbook of China and the change in S. aureus count in lettuce from farm to table described using a predictive model describing the growth of S. aureus in lettuce.

The detection rate of S. aureus in greenhouse soil was 0.04%, at levels of -8.72 to 3.01 (lg(CFU/g)). The average concentration of S. aureus in lettuce to be consumed, which underwent irrigation, harvest, transportation, sale, purchase, storage and washing was -1.95 (lg(CFU/g)) with a 90% confidence interval of -8.98 to 4.40 (lg(CFU/g)). In China, the probability of S. aureus poisoning caused by the consumption of raw lettuce was estimated to be 2.72 × 10^-4 with a mean probability of 7.7 illness per 10 million servings per year. The sensitivity analysis showed that the initial concentration of S. aureus in the soil had the biggest effect on the contamination level of S. aureus in lettuce, followed by household storage temperature and washing before consumption. It is concluded that controlling lettuce-planting environment, rational use of refrigerators, and washing lettuce in a scientific way can reduce the risk of S. aureus food poisoning caused by the consumption of raw lettuce.