Food poisoning outbreak at a bank cafeteria: the investigation report

Abstract number: 1134_03_81

Hanna N., Sarafian A., Mokbel M., Daoud Z., Adib S.

An investigative group was called on 26/5/04 by the Ministry of Public Health to investigate a food poisoning outbreak which had occurred at the central office of one of the biggest banks in Lebanon. The first symptoms of gastro-enteritis compatible with food poisoning appeared among bank employees in the evening of 17/4/04. On that day, many employees had eaten at the bank cafeteria. All of those with signs and symptoms shared the fact that they had eaten the main dish of ‘poulet aux nouilles’. In at least one case, the ‘poulet aux nouilles’ was the only food item consumed at the cafeteria. Of the 32 contacted persons, 26 people eventually reported signs and symptoms compatible with food poisoning; The attack rate for this outbreak was thus very high at 81%, suggesting a very large infective dose ingested in the incriminated dish. Most commonly reported signs are shown in Table 1. In one case, severe septicemia occurred. These findings are compatible with acute salmonellosis. The diagnosis of salmonellosis was confirmed with stool and blood cultures within 48–72 hours after hospital admission of first cases. Investigation of the source: All 18 kitchen workers were subjected to a sampling of rectal and nasal mucosa to be cultured at the laboratory of the Saint-Georges Hospital (HSG) in Beirut.

Results confirm the absence of Salmonella carriage in all. At the time of the outbreak, water was provided from a tanker company. Water samples were repeatedly done on May 18 and 21 yielding high fecal coliform counts but no Salmonella. Different food samples were collected from different batches. A portion of left-overs of the ‘poulet aux nouilles’ dish which was sent out on 18/5/04 revealed the presence of Salmonella on 7/6/04, thus confirming the contamination of the dish. As per the chicken analysis, two specimens heavily grew Salmonella from the surface and internal tissues of raw chicken. Genetic studies have been done on the different isolated strains from chicken, leftovers, and patient, showing clear genetic similarity (Salmonella enteritidis) and suggesting therefore the same origin: chicken.

Frequency of signs and hospitalization following the outbreak (N = 32)

Conclusion:  

Based on our results, the source of contamination was raw chicken. It is important to protect the public from contaminated raw chicken, and to investigate sources of contamination at the chicken farm level.