Gastroenteritis outbreak among attendees of a reconciliation banquet in Riyadh, Saudi Arabia.

On Monday 14 May 2007, 70 persons attended a reconciliation banquet at a house in Riyadh city. The following day, 50 of the attendees started to complain of diarrhea, abdominal pain, fever, nausea, vomiting, chills and headache with some variations in symptoms and severity; 25 sought medical care at emergency departments in different hospitals. This was notified to the on-call center, and an investigation was initiated. The investigating team was comprised of members of the Field Epidemiology Training Program, Ministry of Health and Municipality. A retrospective cohort study was conducted to identify food items and other contributing factors responsible for the outbreak. A structured questionnaire was designed including identification data, consumed food and presenting symptoms. The relative risk, attack rate and the 95% confidence interval (95% C.I.) for each food item and for each restaurant were calculated. The laboratory results of food items, food handlers and of cases were obtained. Data was collected via telephone calls, and were able to contact only 29 of the attendees, of whom 18 were males (62%) and 11 females (38%) (male to female ratio 1.6:1). All were Saudi nationals.

A case was defined as any person who had eaten at the reconciliation banquet on the 14^thof May 2007 in Riyadh and developed diarrhea and one or more of the following symptoms (vomiting, abdominal pain and fever) within two days of food consumption. Diarrhea was defined as three or more loose motions per 24 hours. Out of the 29 persons contacted, 18 were defined as cases (62%) and 11 as non-cases (38%). Out of 18 cases, 12 were males (66.7%) with male to female ratio of (2:1). Out of 11 non-cases, there were 6 males (54.5%) with male to female ratio of (1.2:1). The ages ranged between 11-50 years (mean 28.6 years, SD ± 12.7). The attack rate was higher among males (A.R=66.7) than females (A.R=54.5). Among cases, 100% complained of diarrhea, 88.9% of abdominal pain, 88.9% fever, 77.8% vomiting, 27.8% headache, 22.2% chills and 22.2% nausea. There were neither hospital admissions nor deaths among the cases. The time lapsed between food consumption and onset of symptoms ranged between 7 to 23 hours (mean 12.38, ± SD 4.7 hours).

A line list of food items that all attendees had eaten at the banquet in addition to the time lapsed between food consumption and onset of symptoms are demonstrated in figure 1.

On enquiry, it was found that the restaurant chain which catered the banquet consisted of 8 restaurants and one main center for food preparation. There were 800 people working in this chain. The implicated restaurant was visited and inspected for general sanitation, and food handlers were interviewed and examined for their level of hygiene and presence of health problems. Open-ended questions were asked about different stages of food preparation, storage and delivery. The team inspected the health certificates of food handlers and obtained rectal, nasal, throat and fingernail swabs for laboratory investigations (32 samples), and eight samples (nasal, throat, rectal & fingernails) taken from butchers in the main restaurant. Samples were randomly collected from foods, utensils and refrigerators. Four samples were obtained from utensils in the main food preparation site at the restaurant, in addition to 15 random samples from food items in the suspected restaurant. All samples were sent to the central laboratory of Ministry of Health in Riyadh. The food specific attack rate (A.R), relative risk (R.R) and 95% confidence intervals (95% C.I.) for each food item were calculated (table 1). Um Ali desert had the highest RR 1.93 followed by green salad 1.85.

Regarding laboratory results; 5 cases gave positive results for Salmonella D. Food items, utensils and food handlers gave negative results. The causative organism of this food-borne outbreak was most likely Salmonella D.

It is well known that Salmonella multiplies rapidly in optimal circumstances within temperatures that range from 7^oC to 46^oC.² Regarding the incriminated food items, Um Ali desert is prepared under high temperatures exceeding 75^oC for over 12 minutes, under which Salmonella cannot survive.³ Contamination of Um Ali therefore occurred during transportation or at home. The main component of Um Ali desert is milk, which, whether raw or incompletely pasteurized, can cause infection from several pathogens,most commonly Salmonella and campylobacter,but also from E.coliand L. monocytogens,among others.^4,5 On the other hand, green salad is not exposed to high temperatures, so contamination of the salad may have occurred during preparation, transportation or at home, most probably by cross contamination.

The incriminated food item for this outbreak was probably Um Ali. Green

salad may have been cross-contaminated. An asymptomatic carrier, most likely within the family hosting the banquet, was most likely the source of the organism. The mode of transmission is probably person to person.

Table 1: Attack rates, relative risks & 95% Confidence intervals of consumed food items in a reconciliation banquet in Riyadh.