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Salmonella enteritidis Outbreak, Riyadh, 1999.


On June 23, 1999, eight persons presented to the emergency room of Riyadh Medical Compound complaining of abdominal pain, diarrhea, vomiting and fever. An epidemiological investigation was started to determine the source and extent of the outbreak.


A case-control study was conducted. A case definition was developed, further cases were identified and controls were selected. The cases and controls were interviewed. The restaurant was visited and its staff was interviewed. Food samples and samples from restaurant employees were taken. Stool specimens and rectal swabs were sent to the laboratory for 23 (82.1%) cases.


A total of 28 cases of gastroenteritis and 9 controls were identified. Abdominal pain, general weakness and diarrhea (100%) characterized the gastroenteritis. Fever and headache were present in 92.9% of the cases while 78.6% had nausea and vomiting and only 25% of the cases had chills. The cases and controls had eaten chicken shawerma the night before their symptoms started from the same restaurant and at the same time. However, only the cases had eaten mayonnaise. The average incubation period was 15 hours. There was a strong association between eating mayonnaise and illness (OR was ?, p-value 0.000). No association was found for the chicken (OR could not be calculated), pickles (OR 0.75, p-value 1.0), potato (OR 0.95, p-value 1.0) and ketchup (OR 0.24, p-value 1.0). Salmonella group D was isolated from stool specimens of 8 cases (34.8%).


The Clinical picture and laboratory results suggest that this outbreak was caused by Salmonella enteritidis. Epidemiological evidence indicated that the restaurant-made mayonnaise was the source of infection. It was recommended that restaurants use commercial mayonnaise, and public awareness increased regarding the high risk of Salmonellosis when raw eggs are used in the preparation of mayonnaise.