CFSAN and the USDA’s Agricultural Research Service are conducting research to better understand the factors, including seasonal effects, that could be contributing to E. Coli O157:H7 outbreaks linked to bagged romaine lettuce. FDA and USDA scientists presented findings in the BMC Environmental Microbiome, which revealed that E. Coli O157:H7 survived “significantly better in cold-stored packaged romaine harvested in the fall than on the same varieties harvested in late spring.” In addition, the researchers showed that the microbiome present on bagged lettuce changes based on the season, level of deterioration of the lettuce and whether survival of the pathogen on the lettuce was high or low. They also found that the pathogen survived better in lettuce that was harvested in the fall versus lettuce harvested in the spring during cold storage. “This is a significant step toward closing the knowledge gaps identified in the FDA’s Leafy Greens STEC Action Plan and helping the agency and its partners to reduce foodborne illness linked to the consumption of leafy greens,” CFSAN stated in an agency update.

The study, “Seasonality, shelf life and storage atmosphere are main drivers of the microbiome and E. coli O157:H7 colonization of post-harvest lettuce cultivated in a major production area in California”, has been published on the Environmental Microbiome’s website.