On 12/11/1416 (31 March 1996), 154 students (attack rate 14%) at the girls' college (enrollment 1071) in Sakaka, northern Saudi Arabia developed gastroenteritis. The accident occurred during the final examination week forcing postponement of the examinations. All ill students ate breakfast daily in the college cafeteria. We started the outbreak investigation to determine the source of infection.
Methodology
We defined outbreak associated gastroenteritis as the acute onset of three or more loose stools per day for one or more days during examination week in a student who had eaten in the college cafeteria. We used the college enrollment list to identify students' case-records at the local hospital emergency room. We selected 154 control students from the same enrollment list randomly. We distributed a self- administered questionnaire to case and control students. The questionnaire covers illness and foods eaten from the cafeteria and we compared their frequencies of exposure to different foods and drinks. We interviewed food handlers of the restaurant that supplies food items to the cafeteria.
Results
Gastroenteritis was characterized by diarrhea (100%) lasting from one to three days (median = 1.3), fever (median = 37.8 C), abdominal pain (78.5%), and vomiting (64%). Salmonella was isolated from the stools of four patients. Among 29 food and drink items served during the day before the peak of the outbreak, falafel sandwiches were associated with gastroenteritis (odds ratio [OR] = 7.9; 95% confidence interval [CI] 4.3-14.7). Among the four different combinations of ingredients for these sandwiches, only falafel with cucumber was associated with gastroenteritis (OR = 11.2; 95% CI 6.1-21). The worker who sliced the cucumbers had onset of diarrhea five days earlier and Salmonella was recovered from his stool. After he sliced the cucumbers he kept them in a plastic bag at room temperature for seven hours before assembling the sandwiches.
Conclusion
This outbreak of salmonellosis probably resulted from contamination of cucumbers by an ill food worker and multiplication of the pathogen during seven hours at incorrect storage temperatures. Food handlers should not work with food when ill with diarrhea.