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Food Borne Outbreak in Bisha City, Saudi Arabia, May 2007.


On Thursday 03 May 2007 at about 9 am many patients started to arrive at the emergency department of King Abdullah Hospital in Bisha city. All of the patients mentioned a history of eating meals on the afternoon through midnight of Wednesday 02 May from the same restaurant. We started an investigation to identify the food item responsible for the outbreak and determine the source of infection.


We conducted a case control study. A case (patient) was defined as anyone who ate from the same restaurant on 02 May and developed one or more of the following symptoms: diarrhea, nausea, vomiting, abdominal pain, and fever. The controls were those who accompanied the cases and shared them having eaten food from the same restaurant. We took a sample of 55 cases and 55 controls and asked them about food consumption and symptoms and admission history.


81.8% of the cases were more likely than controls 5.5% to have eaten the Russian salad with mayonnaise (Odds ratio OR = 78; 95% Confidence Interval CI = 20.21-301.04). Eating Mutabel and Shawirma was found to have association (eating Mutabel Odds Ratio OR = 34.2; 95%Confidence Interval CI = 7.57-154.80), (eating shawirma Odds Ratio OR = 3.1; 95%Confidence Interval CI = 1.09-8.62). Salmonella isolated from 51 patients had serotype enteritidis. Out of the 51 positive patients, 29 were positive for stool culture, 22 were positive for rectal swab. Of the food handler rectal swabs done salmonella enteritidis serotype was positive for 5 of them. Mayonnaise was prepared inthe restaurant by adding egg yolks to oil and vinegar and blending them together. After preparing the mayonnaise they mixed it with carrot & cabbage to form the Russian salad and put it in medium plastic packages and then distributed these with each roasted chicken meal. Russian salad stays in the plastic packages for more than 3 hour at room temperature.


On the basis of this investigation, it is obvious that Salmonella entiritidis was the cause of the outbreak; however immediate source and reservoir could not be clearly identified. Russian salad and/or mutabal were the most probable immediate sources of infection. Reservoir could be either raw eggs used in mayonnaise and added to Russian salad and reached mutabal through cross contamination; or the food handlers themselves contaminating both foods.