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An institutional outbreak of Salmonella enteritidis in Singapore
1Quarantine and Epidemiology Department, Ministry of the Environment, Singapore.
Abstract:
A large outbreak of food poisoning occurred in Singapore in March 1995 when a total of 188 inmates in an institution was taken ill. Salmonella enteritidis was isolated from the stool cultures of 35 inmates (16 symptomatic and 19 asymptomatic). All the isolates were of the serotype profile 0:1, 9, 12 and H:g, m (antigen phase I); all were sensitive to ampicillin, ceftriaxone, chloramphenicol, co-trimoxazole and ciprofloxacin. Plasmid profile analysis and restriction enzyme fragmentation patterns (REFPs), as generated with EcoRI and HindIII, of a 60 kb plasmid obtained from these isolates were all identical, confirming that the outbreak resulted from a single source of infection. Stratified statistical analysis of food-specific attack rates strongly implicated imported canned luncheon pork consumed by the inmates on 26 March 95 as the single most probable cause of the food poisoning [p < 10(6), Mantel-Haenszel weighted odds ratio (OR) = 14.33; 95% confidence interval (CI) = 6.20-33.15]. The median incubation period of this outbreak was 19.3 hours and the median duration of illness was three days. The outbreak was rapidly brought under control through prompt implementation of epidemic control measures which comprised active search for diarrheal cases, rectal swabbing of asymptomatic inmates, isolation of those found to be infected, and maintenance of a high standard of personal, food and environmental hygiene.
Insights
A 1995 Singapore food poisoning outbreak sickened 188 inmates. Imported canned luncheon pork was identified as the likely source of Salmonella Enteritidis infection.
Area of Science:
- Foodborne illness epidemiology
- Microbial outbreak investigation
- Public health surveillance
Background:
- A significant food poisoning outbreak affected 188 inmates in a Singapore institution in March 1995.
- Salmonella Enteritidis was identified as the causative agent, with specific serotype and antimicrobial susceptibility profiles noted.
Purpose of the Study:
- To investigate the source and epidemiology of a large foodborne outbreak.
- To identify the specific food vehicle responsible for the outbreak.
- To document the control measures implemented.
Main Methods:
- Bacteriological analysis of stool samples to isolate and identify the pathogen.
- Plasmid profile analysis and restriction enzyme fragmentation patterns (REFPs) for strain typing.
- Stratified statistical analysis of food-specific attack rates to pinpoint the implicated food source.
Main Results:
- Salmonella Enteritidis (serotype 0:1, 9, 12 and H:g, m) was isolated from symptomatic and asymptomatic inmates.
- Identical plasmid profiles and REFPs confirmed a single source of infection.
- Imported canned luncheon pork was statistically implicated as the most probable cause (p < 10(6), OR = 14.33).
- Median incubation period was 19.3 hours; median duration of illness was three days.
Conclusions:
- The outbreak was definitively linked to contaminated imported canned luncheon pork.
- Prompt epidemic control measures, including case finding, isolation, and hygiene, were effective in controlling the outbreak.
- This investigation highlights the importance of food safety and surveillance in preventing large-scale foodborne illnesses.