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Foodborne Salmonella outbreak in a college, Riyadh, Saudi Arabia, October 2009 (1430 H).

On Tuesday 27th October 2009 at 11 a.m., many students from a college in Riyadh presented to the college polyclinic with symptoms of gastroenteritis, including diarrhoea, abdominal pain, nausea, vomiting and fever. Out of them, 77 were referred to different hospitals in Riyadh where they were admitted, received the proper management and discharged without any complications. Following this incident, concerned authorities at the college restricted the served meals to yoghurt and white cooked rice for the following two days. Cases continued to appear over the following three days to reach 200 reported cases. A line listing of all affected students was made. The directorate of health affairs in Riyadh received notifications from the corresponding hospitals and the polyclinic of the college. In response to these notifications, a team from Field Epidemiology Training Program was assigned to investigate this outbreak on Saturday 31st October 2009.
The team visited the concerned hospitals, where all affected students had already been discharged. Their medical records were reviewed for demographic data, clinical presentation, lab investigations, and duration of hospital stay. The team visited the college polyclinic and some of the affected students were interviewed about their symptoms and signs, what they ate in the last 2 days and what they think about the implicated food item(s). This was done in order to confirm the diagnosis and decide on the case definition. They all gave history of eating food from the restaurant of the college, which is the only place for dining in the college.
A case control study was conducted to identify the implicated food item(s). A case was defined as any student who ate from the college restaurant between 26/10/2009 to 29/10/2009 and developed diarrheal illness within three days of food consumption. A control was defined as any student who ate from the same restaurant at the same time period and did not develop diarrheal illness. Self administered questionnaires were distributed to study subjects to collect information about food items, symptoms, and admission history.
A total of 140 cases and 140 controls were enrolled in the study. Out of 140 cases, 95.7% presented with diarrhea. Fever was reported by 87.9%, abdominal pain by 87.1%, nausea by 51% and vomiting by 36.4% (Figure 1). Among food and
drink items served on the three meals of Monday 26th of October and Tuesday’s breakfast on 27th of October, there was a strong association between illness and eating Umm Ali Sweet, which was served on Monday’s dinner (OR= 10.5, with 95% C.I 6.0 - 18.2).
The first case had onset of symptoms at 07:00 am on Tuesday 27th October 2009, while the last case had onset at 10:00 am on Thursday 29th October. Considering the dinner served on Monday 26th October 2009 as the incriminating meal, the mean incubation period was 19.95 hours (range 10-61 hours). The epidemic curve was typical of a point source outbreak (Figure 1).
On further enquiry, the implicated Umm Ali sweet was prepared from “puff pastry”, milk powder and sugar. Puff pastry dough was prepared at the college restaurant at 9:00 from unpasteurized raw eggs, water and flour. Then it was cut into slices and placed in the oven for a few minutes. After that, these slices were kept at room temperature, till around 4:00 pm, when they were mixed with milk and sugar and placed again in the oven for another few minutes. Then it was kept at room temperature for 2 hours to be served at 7:00 pm, while the students started arriving for dinner at 9:00 p.m. The maximum temperature on Monday 26th October 2009 was 33oC and minimum 25oC, providing favorable conditions for microorganism growth.
The college restaurant was a double storey building. The first floor comprised the dining hall and the ground floor was used for food preparation (Kitchen), food storage and cleaning of cooking utensils. The dining hall had a total area of approximately 1200 m2 and consisted of 200 tables that can accommodate 1600 students at one single time. All students took their three meals at this dining hall at fixed times. On inspection of the dining hall, it was clean, well organized, ventilated and illuminated. Food preparation was done in different sections; one for preparation of salads, another for desert and the third for hot meals. Each section had its own employees and appliances.
No leftover food was available for laboratory examination. There was no history of recent diarrhea or isolation of Salmonella from the food handlers before the outbreak, and all of them possessed a valid health certificate. Cultures taken from 104 food handlers grew Salmonella enteritidis group D among 3 (2.9%) food handlers who had developed gastrointestinal symptoms. In addition, five (2.5%) students who agreed to give stool or rectal swab specimens were also positive for Salmonella enteritidis group D. The same organism was also grown from a swab taken from one food utensil.

Editorial note:

Foodborne diseases are a group of illnesses resulting from consumption of contaminated foods or beverages. Most of these diseases are infections, caused by a variety of bacteria, viruses, and parasites. Other Foodborne diseases are poisonings, caused by harmful toxins or chemicals that have contaminated the food.1

In the present outbreak, dinner on 26th October 2009 was the common meal responsible for the outbreak and the restaurant-made “Umm Ali” sweet, prepared from infected eggs was the incriminating food item on the basis of the highest statistically significant odds ratio. Moreover, unsafe storage of “Umm Ali” sweet at room temperature and the long interval between its preparation and the time dinner was served made it possible for bacterial multiplication. Unfortunately, there was no direct evidence since no samples of food served at the dinner were available for microbiological analysis.
The clinical and epidemiological features give important clues to etiology. Nausea and vomiting occurring within 1-6 hours of food ingestion point to either Staphylococcus aureus or Bacillus cereus. However, fever is a relatively uncommon symptoms with these two microorganisms.2 In this outbreak, the median incubation period was 27 hours and 87.9% of the cases had fever; making Staphylococcal and Bacillus cereus food poisoning unlikely.
Abdominal cramps and diarrhoea within 8-16 hours can occur in Clostridium perfringens food poisoning. However, although nausea can occur, vomiting and fever are uncommon.3 In the present outbreak, 36.4% had vomiting and the majority had fever (87.9%), therefore Cl. perfringens food poisoning was also excluded.
Fever, abdominal cramps, and diarrhoea within 6 to 48 hours, as in the present outbreak, are usually due to Salmonella, Shigella, and Campylobacter jejuni.4 Shigella can be excluded, as there was no blood in the stools in the majority of the cases. Campylobacter jejuni is characterized by vomiting inonly 15-25% of the cases.5 Its incubation period is also longer, 1-7 days.6 Therefore Campylobacter jejuni also can be excluded.
On the basis of this investigation, this foodborne outbreak was caused by Salmonella enteritidis. Umm Ali sweet was the implicated food item. Raw eggs were the most likely source of infection, while time-temperature abuse during preparation and storage of Umm Ali sweet was the most important contributing factor.

1.Center for Disease Control and Prevention. Fact sheet: Foodborne illnesses. Atlanta. Available from URL:

2.Heymann CJ, MD, editors. Control of Communicable Diseases Manual. 18th ed. Washington (DC): American Public Health Association; 2004:211-216,469-473.

3.Tauxe RV, Swerdlow DL, Hughes JM. Food borne diseases. In: Mandell, Douglas, and Bennett’s Principles and Practice of Infectious Diseases. Edinburgh: Churchill Livingstone, 2000; 1150- 65.

4.Giannella RA, Formal SB, Dammin GJ, et al. Pathogenesis of salmonellosis: Studies of fluid secretion, mucosal invasion, and morphologic reaction in the rabbit ileum. J Clin Invest 1973; 52:441.

5.Blaser MJ, Checko P, Bopp C, et al. Campylobacter enteritis associated with foodborne transmission. Am J Epidemiol 1982; 116: 886.

6.Tauxe RV. Epidemiology of Campylobacter jejuni infections in the United States and other industrialized nations. Washington DC: American Society of Microbiology; 1992; 9-19.