When cooking is not enough: microbial contamination dynamics and Salmonella infection risk in street-vended grilled chicken under real vending conditions in Benin, West Africa

Abstract

Foodborne diseases remain a major public health concern, particularly in low- and middle-income countries where street-vended foods are widely consumed. This study evaluated the microbiological quality and Salmonella infection risk associated with street-vended grilled chicken skewers in Benin using field observations and quantitative microbial risk assessment (QMRA). Hygiene practices, handling behaviors, and time-temperature profiles were documented among 135 vendors. Three skewer categories were collected from 45 vendors ( n = 45 each): raw skewers, freshly grilled skewers without condiments, and freshly grilled skewers with condiments, all from the same production batch. An additional 90 ready-to-eat samples were collected during the selling period from foods displayed for sale at different post-cooking holding times (<2 h, 2–4 h, and >4 h after cooking). These samples were used for field-based risk estimation and comparison with QMRA outputs. Salmonella spp., Escherichia coli , and Staphylococcus aureus were quantified, with Salmonella confirmed by PCR targeting the invA gene. Poor hygiene was widespread, including unrefrigerated transport, ambient holding, shared utensils, bare-hand handling (98.6%), and lack of handwashing before serving (76.3%). Raw skewers exhibited high contamination (TVC: 8.7 ± 0.5 log CFU/g), indicating substantial pre-cooking microbial burden. Cooking reduced E. coli and eliminated detectable Salmonella . However, freshly grilled products still showed notable residual contamination (TVC: 5.4 ± 0.4 log CFU/g; E. coli : 2.7 ± 0.5 log CFU/g ). Salmonella was detected again immediately after condiment addition and increased during vending, while S. aureus was present in all samples. During retail, microbial counts increased, indicating progressive post-cooking amplification. Across consumption scenarios, the median daily probability of Salmonella infection per consumer was 1.0 × 10⁻³, corresponding to 314,586 infection cases per million consumers per year overall, 8,747 cases per million consumers per year for freshly prepared skewers consumed on-site, and 769,671 cases per million consumers for take-home consumption without reheating. Field-derived estimates were consistent with QMRA predictions. These findings demonstrate a dual contamination pathway in street-vended grilled chicken, where high pre-cooking microbial loads combine with post-cooking recontamination to sustain exposure. Grilling does not act as a terminal safety barrier in informal vending systems. Effective risk reduction therefore requires interventions targeting the entire production-to-vending continuum, beyond temperature control alone.