On November 12, 1995, a Riyadh city hospital reported 18 patients with gastroenteritis all of whom had attended wedding receptions in three different wedding halls on November 8. We began an investigation to determine the extent, and the cause of the outbreak.
Methodology
A case of gastroenteritis was defined as an acute onset of diarrhea (more than 3 loose stools per day) after attending one of the three weddings. We identified 49 families who attended any of the three weddings and determined the food and drink exposures at the weddings and illness histories for all family members. Attack rates of gastroenteritis by exposure to different food and drink items at the weddings were compared.
Results
Among the 284 persons from the 49 families contacted, 92 developed gastroenteritis (attack rate [AR] = 33%), between 5 to 57 hours (mean 18) after eating at the wedding banquets. Salmonella was isolated from stool in 24 cases. In all three weddings, gastroenteritis affected only the 208 family members who ate from a supplemental buffet served to women and children (AR=45%) which was prepared by a single caterer at all three weddings. Nine of 43 different buffet food items all containing ground mutton, or ground chicken were associated with gastroenteritis with risk ratios (RR) ranging from 1.3 to 2.8 for ground mutton kebab. Eating any food made with ground mutton gave a RR = 5.8 (95% CI 3.0 -11). Food items made with ground or boned chicken were not associated with gastroenteritis after stratification with ground mutton, and persons who ate only chicken food items did not develop gastroenteritis. All ground mutton foods were prepared from rapidly thawed (under one hour) frozen ground mutton that was reground in the same meat grinder after thawing. After cooking, ground mutton food items were held at ambient temperatures for two to four hours at the caterer's and then kept warm on serving trays that were heated by flames for another three to four hours at the wedding halls.
Conclusion
This outbreak of salmonellosis was caused by food items made from ground mutton prepared by one caterer and served at three weddings. Three major defects in food handling, inadequate thawing, cross contamination before and after cooking, and warm holding temperatures after cooking, contributed to this outbreak. Serving large groups at weddings, and other gatherings is a common practice in Saudi Arabia.