A case study of critical points for the entry and spread of Salmonella Infantis in a broiler farm.

Salmonella Infantis is a zoonotic pathogen that frequently persists in broiler production systems, posing a risk to food safety and animal health. Understanding its entry and spread in these systems can inform control measures and reduce contamination.A longitudinal field study (2021-2022) was conducted on an eight-house broiler farm managed by three farmers to identify critical contamination points for S. Infantis. In 2021, 49 out of 536 samples (9.1%) were positive for S. Infantis, with the highest contamination rates found in anterooms (11.7%), the farm exterior (9.1%) and in the production area (7.5%). Only two out of 196 samples were positive after the implementation of cleaning and disinfection (C&D) measures. After destocking, 5.9% of samples tested positive for S. Infantis. The critical points with the highest contamination rate were litter, ventilation systems and nipple cups in the production area, floor and equipment in the anteroom and farm exterior. When the farm was revisited in 2022, S. Infantis was detected in four houses after the fattening cycle was completed, although there was no contamination prior to flock arrival. Whole-genome sequencing of 69 isolates showed that all isolates harbored the pESI plasmid and belonged to ST32. Clonal S. Infantis isolates mostly originated from houses managed by the same farmer, with occasional cross-contamination between houses managed by different farmers. Although persistent strains were frequently observed, the introduction of a new strain into previously negative houses was also observed.This study highlights that strict and consistent adherence to C&D protocols is critical for effective control of S. Infantis spread within and between flocks. Persistent contamination in certain areas highlights the need for targeted interventions at identified critical points.