Outbreak of Salmonella Gastroenteritis among Guests in 3 Wedding Halls, Riyadh, 1995

On November 12, 1995, a Riyadh hospital reported 18 patients with gastroenteritis. All had attended wedding receptions in three unrelated wedding halls on November 8. Other hospitals were alerted and by November 15, 83 gastroenteritis cases had been reported all among children below 12 years of age and females persons attending three wedding halls Salmonella enterica (Serogroup D) was recovered from the stool of 25 of the 83 reported. Although the three wedding halls were unrelated, all served a buffet for females that had been prepared by one caterer.

A retrospective cohort study was conducted to determine the foods responsible for the outbreak. Gastroenteritis was defined as the acute onset of diarrhea (more than three loose stools per day) after attending one of the three weddings. From 265 families that attended these weddings, 49 were contacted. We determined gastroenteritis symptoms and food and drink consumed at the weddings for 284 family members in these families. Of the 284 persons, 92 (Attack rate=32%) developed gastroenteritis within 6 to 57 hours (me °an 18 hours) after eating at the wedding banquets. All developed diarrhea; 73% reported vomiting; and 90% had fever (mean 38.8°C); 65% had chills. The median duration for illness was four days (range 1-9 days). Symptoms developed in the 90% of the patients within 6 to 24 hours, and no longer than 2.5 days after the weddings. For all three weddings, gastroenteritis affected only those who attended the female and children's section and who ate from a supplemental buffet prepared by the caterer (AR = 45%). Attack rate among women and children was 35% in hall A, 59% in hall B, and 42% in hall C.

Comparison of food specific attack rates for foods served showed that eating cooked foods prepared by the caterer was associated with gastroenteritis (AR= 51%, Risk Ratio [RR]=14, 95% confidence interval [CI]=3.6-55<0.0000). Food prepared by the wedding halls and salads and desserts from the buffet were not associated with gastroenteritis. The caterer served 24 cooked dishes. All nine food items made of ground mutton were associated with development of gastroenteritis with RR range from 15 (95%CI= 6.5-33) for edam mosaqaa to 8.1 (95%CI= 3.2-20) for the kobah (Table 1). Also ground chicken kofta and hot dog slices were associated independently with development of gastroenteritis illness with RR of 2.5 (95% CI = 2.0-3.3) and RR of 2.0 (95%CI=1.5-2.7) respectively. Guests who ate only from the 13 other cooked foods did not develop gastroenteritis.

The incubation period was increased by 4.9 hours for each addition food item consumed containing ground mutton (r = -0.63, 95% CI = -0.74, -0.48 ). The attack rate for developing gastroenteritis also increased as the number of food items containing ground mutton consumed increased from 8% for guests who ate cooked foods which did not contain ground mutton to 43% for one ground muttom item and reached 100% for four or more ground mutton items (P <0.001, Chi Square for trend).

Thawed ground chicken used to make the chicken kofta was first reground in meat grinder. The thawed (<1 hour ) ground mutton was then run through the same meat grinder. All ground mutton was first cooked in single container and then used in preparing the nine different food items. After cooking, the ground mutton food items and other cooked foods were held at ambient temperatures for two hours at the caterer's establishment and in his delivery van. At the wedding halls they were kept warm on serving trays for another three to four hours before eating.

Salmonella is found in a wide variety of raw animal products including meat, eggs, and milk. Prevention of foodborne salmonellosis requires complete cooking to kill salmonella, clean utensils and surfaces to avoid cross-contamination of raw and cooked food, and storage of cooked food at temperatures above 60° C or below 4° C. In this outbreak all three of these preventive measures were violated.

Table 1: Food specific attack rates among 233 guests ( 92 gastroenteritis cases) for cooked foods prepared by one caterer for three wedding halls on Wednesday, 8 November 1995.Riyadh, Saudi Arabia.