On Tuesday 02 June 2009, an increased number of patients complaining of food poisoning symptoms started to arrive after 10 pm at the emergency department of King Fahad hospital in Al-Hofuf city, and through the following two days. All the patients mentioned a history of eating a meal from the same restaurant. We started an investigation to identify the food items responsible for the outbreak and determine the source of infection.
Methodology
A case control study was conducted. A case (patient) was defined as anyone who ate from the same restaurant on the 2nd or 3rd of June 2009 and developed one or more of the following symptoms: diarrhea, nausea, vomiting, abdominal pain, and fever. Controls were those who accompanied the cases and shared food from the same restaurant. A sample of 50 cases and 50 controls was selected and asked about food consumption, symptoms and admission history.
Results
Cases (74%) were more likely than controls (3%) to have eaten a food item that contained mixed sauce (Odds ratio (OR) = 44.59; 95% Confidence Interval (CI) = 11.82-168.1). Eating Chicken Shawarma was found to have a significant association with food poisoning (OR = 3.88; 95% CI = 1.43-10.73). Salmonella enteritidis Group "D" (Non typhoid strain) was isolated from 28 patients; 18 (36%) from stool cultures, and 10 (20%) from rectal swabs. Stool cultures of the food handlers were negative. Salmonella was also isolated from some remnants of the mixed sauce prepared at the restaurant. The incriminated mixed sauce was prepared inthe restaurant by blending egg yolks, vegetable oil, cheese, salt, and vinegar in an electric mixer then placed in big plastic containers in the fridge. It is taken out of the fridge at 4 pm and added to sandwiches according to clients' demand. Leftovers of the mixed sauce are often used the following day.
Conclusion
On the basis of this investigation, it is obvious that Salmonella was the cause of the outbreak; however immediate source and reservoir could not be clearly identified. Mixed sauce and/or Chicken shawarma were the most probable immediate sources of infection. The reservoir could have been the raw eggs used in the mixed sauce, which may have reached the chicken shawarma by cross contamination.