US: For safety store packaged salads below 5

Storing packaged lettuce salads at 5 or below is vital to reducing food safety risks, according to a new US study.
The research, published in the Journal of Food Science and led by food technologist Yaguang Luo at the US Department of Agriculture, examined samples of packaged lettuce that had been inoculated with E.coli bacteria, resealed and stored at 5 and 12 until their 'Best if used by Dates.'
The results showed that storing packaged lettuce at 5 failed to eliminate the bacteria, however did limit its growth to within safe levels. Packaged lettuce stored at 12 grew E.coli to statistically significant levels.
According to the authors of the research, food-borne pathogens "can grow significantly on commercially packaged lettuce salads while the product's visual quality is fully acceptable."
The authors noted that while manufacturers fail to effectively remove bacteria during the preparation of packaged salads, many are still marketed as 'ready-to-eat' (RTE).
The authors said specific data regarding the effect of temperature of pathogen growth on leafy greens could help regulators and processors to develop science-based food safety guidelines and practices.