Salmonella Enteritidis Outbreak at a Remote Mining Camp, Omnogovi Province, Mongolia, March 2025

On March 18, 2025, the National Center for Communicable Diseases received reports of acute gastroenteritis among employees at a remote mining company in Omnogovi Province, Mongolia. We investigated this outbreak to identify the likely source, characterize its transmission, and recommend control measures. Utilizing a retrospective case-control design, we interviewed employees regarding their symptoms, restaurant visits, and menu exposures between March 14 and 17. A confirmed case was defined as gastrointestinal illness with Salmonella spp. detected in a rectal swab specimen. We tested clinical, retained-food, environmental, and water samples from Restaurants A, B, and C. Food-specific odds ratios (ORs) with 95% confidence intervals (CIs) were estimated. Of 204 surveyed employees, 68 (33.3%) reported gastrointestinal illness, and 30 (14.7%) satisfied the confirmed case definition. Symptom onset among cases clustered from March 16 to 19, peaking on March 17. Confirmed cases were reported among patrons of Restaurants A (n = 9), B (n = 15), and C (n = 6). Several menu items served from March 14 to 16 were associated with confirmed cases, including kimbap at Restaurant A (OR: 118.2; 95% CI, 11.22-6,245); millet porridge with milk (OR: 40.02; 95% CI, 3.25-2,241); steamed dough soup with garlic (OR: 33.19; 95% CI, 4.79-407); broccoli soup at Restaurant B (OR: 16.08; 95% CI, 2.05-196.8); and dessert at Restaurant C (OR: 16.68; 95% CI, 1.00-1,089). Salmonella spp. was detected in 12 prepared-food samples and on a wooden meat-cutting board, and Salmonella Enteritidis was isolated from clinical specimens. Escherichia coli was also detected on food-contact surfaces. The diverse food associations across multiple restaurants, coupled with environmental contamination, strongly suggest cross-contamination within the shared catering system. This highlights the critical need for enhanced food safety management in remote mining-camp catering operations.