Whole-Genome Sequencing Investigation of a Salmonella enterica Serovar Typhimurium ST19 Foodborne Outbreak in Lvliang, China: Ready-to-Eat Quail Eggs as a Suspected Vehicle

In September 2022, acute gastroenteritis affected 28 people in 10 households in Lvliang, China. Unrestricted interviews identified ready-to-eat quail eggs from one supermarket as the only recurring exposure among the first six households; an exposure-based case definition was adopted thereafter. Descriptive epidemiology, food-hygiene inspection, culture, and whole-genome sequencing yielded eight Salmonella enterica serovar Typhimurium isolates (five patient and three leftover-food). All were ST19/cgST 294557. Assembly-based common-core analysis found 12 variable sites across 4,756,146 callable bp and pairwise distances of 1–10 SNPs; a neighbor-joining tree reconstructed from the same pairwise SNP matrix showed concordant relationships among the eight isolates. Genomic data supported a common outbreak clone but not the original food or contamination direction. Epidemiology implicated ready-to-eat quail eggs as a suspected vehicle, but the exposure-based case definition, lack of an unexposed comparison group or retained retail cooked product, and costorage of positive leftovers precluded definitive attribution.