A Foodborne Disease Outbreak Caused by Salmonella enterica Serovar Braenderup (ST311) - Yangjiang City, Guangdong Province, China, July 2025.

WHAT IS ALREADY KNOWN ABOUT THIS TOPIC?: Salmonella is a major foodborne pathogen, and eggs are established vehicles for common serotypes such as Enteritidis. However, rare serotypes like Braenderup are infrequently identified in outbreaks, partly due to limited routine surveillance and the low resolution of conventional typing methods.

WHAT IS ADDED BY THIS REPORT?: This report documents a point-source outbreak of Salmonella Braenderup ST311 involving 130 cases (attack rate 19.2%, median incubation 17 hours). Sandwich consumption was strongly associated [corrected odds ratio=1,626.7 (Haldane-Anscombe correction); 95% confidence interval: 81.7, 32,360; P<0.0001]. The outbreak strain was isolated from 34 patients, leftover sandwiches, and raw eggs, with cgMLST allelic differences of 0-1. Whole-Genome Sequencing (WGS) linked it to 32 historical sporadic cases and one food isolate, indicating persistent local circulation.

WHAT ARE THE IMPLICATIONS FOR PUBLIC HEALTH PRACTICE?: Eggs can harbor rare outbreak-prone serotypes. Bakeries must separate raw/cooked materials and ensure hand hygiene. WGS was critical for early detection and traceback in this event.