A scoping study characterizing prevalence, risk factor and intervention research, published between 1990 and 2010, for microbial hazards in leafy green vegetables

A scoping study was conducted to identify all published prevalence, risk factor, and intervention research investigating 16 microbial hazards in leafy green vegetables and to evaluate the volume, main characteristics, basic aspects of methodological soundness and/or reporting, and the main knowledge gaps and research needs. Our study included a comprehensive literature search, a replicable two-level relevance screening (abstract and article levels), and a two-phase quality assessment and data extraction (article level). All steps were conducted by two independent reviewers following general principles of systematic review methodology. From the initial 7961 citations, 657 articles were relevant, reporting one or more research themes: prevalence (314 studies), risk factor (472) and intervention research (269). These articles were published in 190 different scientific journals, 15% between 1990 and 2000, and the remaining 85% after year 2000. Sixty-five percent of studies was conducted in the USA, Canada, or Europe. Over 70% of all studies investigated lettuce. Collectively, four leafy greens (lettuce, cabbage, spinach, and fresh leafy herbs) and microorganism (Escherichia coli, Salmonella, Listeria and coliforms) combinations accounted for almost 80% of relevant studies. Forty-one percent of the research was conducted at the processing stage of production. Lack of reporting sufficient data and/or replicable laboratory protocols (first phase assessment) resulted in exclusion of 60% of relevant articles. In total, 231 papers were retained following second phase quality evaluation, and only 152 (20% of all relevant articles) met all ranking criteria. A lack of well designed, executed, and reported prevalence studies with sampled populations representative of the target populations and of experimental studies investigating the efficacy of intervention(s) under real-life conditions was observed. A limited number of articles investigating commonly accepted important risk factors, for example worker hygiene and health, equipment sanitation, and wildlife, was identified. We highlight research areas with the data potentially feasible for full systematic review-meta-analysis methodology and areas warranting additional investigation. The resulting information is necessary for the establishment of evidence-informed guidelines for food safety enhancement.