Salmonella interrupts final exams, Sakaka Al Jouf, March 1996

On 31 March 1996, 18 young women students from the girls college of Sakaka were evaluated in the emergency room of Prince Abdulrahaman Al-Sudairy General Hospital in Sakaka, Al Jouf region for gastroenteritis symptoms including diarrhea, vomiting, abdominal pain, or fever. The hospital notified the regional health affairs (RHA) in Al Jouf and the RHA asked the Field Epidemiology Team to identify the cause of the outbreak.

Using the enrollment list for the female art college students, case-records were identified at the local hospital emergency room. Out of 1071 students, 154 (14%) students, all mid-way through taking final examinations, developed gastroenteritis and visited the hospital(Figure). Gastroenteritis was characterized by diarrhea for all patients lasting from one to three days (median = 1.3), fever (median = 37.8 C), abdominal pain (78.5%), and vomiting (64%). From 7 rectal swabs taken by patients, Salmonella was isolated from four in the hospital laboratory. The mean age of the identified cases was 21 (age ranged from 17 to 29 years) . The affected students reported that they routinely ate morning snack in the college cafeteria.

A case of gastroenteritis was defined as an acute onset of diarrhea (more than three loose stools per day) for one or more days during examination weeks, 31 March through 10 April 1996, in any female student at art college in Sakaka. We selected 154 control-students at random from the same enrollment list. We distributed a self-administered questionnaire to case and control-students which requested information about the nature of illness and foods eaten from the cafeteria from March 31 to April 2. We compared students' frequencies of exposure to different food and drink for one day before and two days after the first case appeared in the hospital. Of 154 students who reported illness, 145 (94.2%) completed the questionnaire.

Students who reported eating cafeteria food on March 31 had a higher risk (odds ratio = 8.1, 95% Confidence interval = 4.2-15 ) when compared to children who ate cafeteria food only on other days.

Among 29 food and drink items served on March 31, falafel sandwiches were associated with gastroenteritis (OR=7.9; 95% CI=4.3-14.7). Falafel sandwiches contained cucumber, tomato and potato. However many students removed ingredients they did not like. Students who left cucumber in their sandwich had a higher risk of illness than students who removed cucumber from the sandwiches (Table). Only falafel with cucumber was associated with gastroenteritis (OR = 11.2; 95% CI 6.121).

One restaurant supplied the college cafeteria daily with 400 falafel sandwiches. No food remained from the outbreak period but tables and knives were swabbed. All five restaurant employees were interviewed and rectal, nasal, throat, fingernail swabs and stool samples were taken. Salmonella was not isolated from any of these swabs. The employee who sliced the cucumbers was employed as a driver and had no health certificate and had not been examined for Salmonella infection. He gave a history of onset of diarrhea five days before the outbreak. Salmonella was isolated from his stool. He reported slicing the cucumbers beginning on 31 March and for the following three days. He then placed sliced cucumbers in a plastic bag and left them at room temperature for seven hours before assembling the falafel sandwiches.

From this outbreak we see how illness in a food handler can spread, thereby affecting a large number of people. This outbreak shows that ill food handlers, particularly those with diarrhea must be prevented from participating in food preparation while they are symptomatic. The storage of the cucumbers in a plastic bag at room temperature for several hours gave the optimum condition for Salmonella multiplication. A high infective dose was probably reached and resulted in this large outbreak.

Education in proper food handling and storage techniques is needed. In this outbreak education was disrupted and exams were delayed. Health education is also needed to inform management of food preparation establishments, food handlers, and the public of food borne disease.