On June 23, 1997, 36 patients presented to a public hospital in Riyadh, Saudi Arabia, with colic, diarrhea and vomiting. All patients reported eating food from one fast-food restaurant the previous day.
Methodology
A case was defined as any individual who ate from the restaurant on June 22, 1997, and developed diarrheal illness (≥ 3 stools per day) between June 22 and 25. We searched hospital and emergency-room records in the hospital, other hospitals and health centers in southwest and central Riyadh for other cases. We also interviewed patients and unaffected family members about food eaten from the restaurant. We calculated food-specific attack rates and relative risk (RR) for each food item. We reviewed the usual daily routine of food preparation, storage, handling, and the exact constituents of each item served.
Results
Of 142 identified cases, 91 (64%) were traced and interviewed. All 91 cases patients interviewed had diarrhea (100%), 98.9% had colic, 93% had vomiting, 84.6% had fever, and 54% were hospitalized. Salmonella group D (non-typhi) isolates were grown from rectal stools or vomitus samples. Salmonella was also grown from an unopened sandwich that was kept overnight in the refrigerator by one family. The median age was 13 years (range = 1-61 years); both males and females were almost equally affected (51.4% and 48.6% respectively). Among 22 families, 94 persons had eaten food from the restaurant on June 22, and 80 were cases (attack rate [AR]=85%). The cafeteria sells only shawarma (hot chicken sandwiches) and hamburgers. The attack rate for persons who ate shawarma was 88%, compared with 0% for those who did not (<0.01 Fisher's exact test). In contrast, persons who ate hamburgers had a lower attack rate (50%) compared with those who did not (RR 0.57; P<0.05). Mayonnaise and salad ingredients used in both hamburgers and shawarmas were not associated with illness. Chickens used for shawarma were thawed in warm water, deboned and marinated at room temperature over seven hours before refrigeration. Marinated chicken is grilled as a large mass on a spit and sliced off the spit as needed. Revision of food poisoning surveillance of the Riyadh city region during the year 1996 showed that of 28 reported food poisoning outbreaks from public places, 10 (38%) were attributed to chicken shawarma.
Conclusion
The association of shawarma with illness and the time-temperature abuse during preparation indicate that chicken in the shawarma sandwich was responsible for this large outbreak. Chicken shawarma is a highly popular food in Saudi Arabia and a safe method of preparation needs to be identified and instituted in all restaurants.