Purpose: The objective of this study was to perform a systematic review of risk factors for contamination of fruits and vegetables with L. monocytogenes, Salmonella, and E. coliO157:H7 at the pre-harvest level.
Methods: Relevant studies were identified by searching 6 electronic databases: MEDLINE, EMBASE, CAB Abstracts, AGRIS, AGRICOLA, and FSTA. Searches were conducted using the following thesaurus terms: L. monocytogenes, Salmonella, E. coliO157 AND fruit, vegetable. All searching terms were exploded to find all related subheadings. To be eligible, studies had to be prospective controlled trials or observational studies at the pre-harvest level and had to show clear and sufficient information on the process in which the produce was contaminated.
Results: Out of 3,463 identified citations, 68 studies fulfilled the eligibility criteria. Most of these studies were on the leafy greens and tomato. While many risk factors for the pre-harvest level produce contamination have been evaluated, the quality assessment of the reviewed studies confirmed existence of solid evidence for only some of them, including produce growing on the clay-type soil, application of contaminated or non-pH-stabilized manure and usage of spray irrigation with contaminated water, with a particular risk of contamination on the lower leaf surface. Weak or missing evidence of association with produce contamination was determined for additional risk factors, including for the effect of animal host’s diet, wild animal intrusion and floods.
Significance: Synthesis of the reviewed studies suggests that reducing microbial contamination of irrigation water and soil are the most promising targets for prevention and control of produce contamination. Furthermore, this review provides an inventory of the evaluated risk factors, including those requiring more research.