Quantitative microbial risk assessment of extended-spectrum β-lactamase-producing Escherichia coli transfer from broiler litter to fresh lettuce consumption

Abstract

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, partitioning, and runoff to rivers; irrigation transfer yielded lettuce contamination for a 100 g serving. We estimated exposure, mapped gastrointestinal colonization to urinary tract infection (UTI) via conditional probabilities, and expressed the burden as disability-adjusted life years (DALYs) per serving. Global sensitivity analyses identified main exposure drivers. Environmental time was indexed as days since litter application and the planting interval denoted days from litter application to planting.

Results

The farm model produced mean end-cycle litter of 1.6 × 10⁴ CFU/g and near-complete flock colonization within one week. Soil surface loads declined from 3.2 × 10⁷ CFU/m² to 8.6 × 10⁵ CFU/m² by day 100. Runoff yielded river concentrations of 6.0 × 10⁻² CFU/mL after 10 days. Exposure from lettuce consumption ranged from 1.7 CFU/100 g to 7.6 × 10⁻³ CFU/100 g; simple household washing cut exposure by ∼90 %. Global sensitivity analysis identified soil-water partitioning and decay rates as the most important parameters of exposure variability. For health endpoints, UTI risk per serving ranged from 4.6 × 10⁻¹² to 9.0 × 10⁻⁹, and DALY per serving ranged between 10⁻¹⁰ and 10⁻⁸.

Conclusions

Predicted health burdens decreased markedly with consumer washing and longer intervals between litter application and lettuce planting. Residual contamination persists, indicating value in evaluating the effectiveness of manure treatments and irrigation-water quality interventions on reducing environmental loads and human risk.