Quantitative Microbial Risk Assessment of Extended-Spectrum β-Lactamase-Producing Escherichia coli Transfer from Broiler Litter to Fresh Lettuce Consumption
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Background
Extended-spectrum β-lactamase-producing Escherichia coli (ESBL E. coli ) from broiler chicken production pose potential public health risks via multiple environmental and foodborne pathways. We developed a modular quantitative microbial risk assessment (QMRA) model linking four components, namely farm, soil, river, and lettuce consumption, to predict human environmental exposure to ESBL E. coli originating from broiler flocks.
Methods
A stochastic farm module simulated broiler colonization over a 36-day cycle and generated end-cycle litter loads. Field modules represented first-order decay, attachment/partitioning, and runoff to rivers; irrigation transfer yielded lettuce contamination for a 100 g serving. Disability-Adjusted Life Year (DALY) estimation characterized health risk and global sensitivity analyses identified main drivers.
Results
The farm model produced mean end-cycle litter of 1.6 × 10 4 (SD 16.1, UI 1.60–1.61 × 10 4 ) CFU/g and near-complete flock colonization within one week. Soil surface loads declined from 3.2 × 10 7 (SD 3.2 × 10 4 , UI 3.2–3.2 × 10 7 ) CFU/m 2 to 8.6 × 10 5 (SD 8.8 × 10 2 , UI 8.6–8.6 × 10 5 ) CFU/m 2 by day 100. Runoff yielded river concentrations of 6.0 × 10 -2 (SD 3.5 × 10 -3 , UI 5.5–6.6 × 10 -2 ) CFU/mL after ten days. Lettuce contamination was highest at short intervals after land application 1.7 (SD 8.5 × 10 -2 , UI 1.5–1.8) CFU/100 g at one day interval, dropping to 0.85 (SD 5.0 × 10 -2 , UI 0.76–0.95) CFU/100 g at day 20 interval; simple household washing cut exposure by ∼90 %. Global sensitivity analysis identified soil-water partitioning and decay rates as most important parameters of exposure variability. DALYs lost ranged from 10 -8 to 10 -10 per serving.
Conclusions
In our scenarios, predicted health burdens varied with ESBL E. coli concentration in irrigation water and intervals between litter application and lettuce planting. While environmental decay and simple measures such as household washing substantially reduce exposure, residual contamination persists. Future studies should evaluate the effectiveness of manure treatments and irrigation-water quality interventions on reducing environmental loads and human risk.
