Food-borne disease outbreak in a boys primary school in Dammam, October 2003 G

On Tuesday 18 Sha'aban 1424 H (14 October 2003 G) a national newspaper reported an incident of abrupt abdominal colic and vomiting affecting more than 35 students at a primary school at the National Guard residence compound (NGRC) in Dammam, Eastern Province, after taking their breakfast from the school canteen the previous day. The Field Epidemiology Program (FETP) decided to investigate this outbreak. The Objectives of the outbreak investigation were to identify cases and the implicated food item(s), determine the factor(s) associated with the occurrence of the outbreak, establish measures to control and contain the spread of the outbreak, promptly recognize the causative agent to allow specific treatment of cases, and place recommendations to prevent future outbreaks. The school where the outbreak occurred was a boy's primary school located within the National Guard Residence Compound (NGRC). It is attended by 539 students and 45 teachers and management staff The school-break lasts from 9:15-9:35 am. The students usually buy their breakfast from the school canteen. On the day of the incident, the teachers noticed a mass complaint of sudden abdominal pain and vomiting among the students; 26 students were taken to the emergency departments of both the National Guard Health Center and the Imam Abdulrahman Al-Faisal Hospital -Dammam, close by.

A case-control study was carried out. Any student who had complained of nausea, abdominal colic, vomiting, diarrhea, or any other gastrointestinal symptoms on the day of the outbreak were brought to the investigative team for interview. A case was defined as any student from the school who had sudden symptoms of nausea, abdominal colic, vomiting or diarrhea, after eating or drinking food or drinks bought from the school canteen on Monday 17 Sha'aban 1424 H. A control was selected randomly for each case from the same class. If none were available then the control was selected from the same grade, or from the next lower grades.

Sixty-seven students met our case definition and were considered as cases, and another 67 were selected as controls. Among the cases, 33 (49.25%) had consulted the health services of the National Guard; almost all were discharged on the same day in good health condition and were completely recovered by the next day, except for one student who needed gastric lavage and another who was hospitalized for 2 days.

The most common symptoms reported were abdominal colic (92.5%), fever (34.3%), headache (34.3%), vomiting (31.3%), nausea (22.4%) and diarrhea (16.4%). Their ages ranged from 6-14 years (median 12 years). Most of the cases were from the 6th grade (68.7%). The Incubation Period (IP) ranged from 15 minutes-8.5 hours, with a median IP = 55 minutes (Figure 1).

Regarding exposure of the cases and controls to food items, a high OR was found for eating za'atar fata'yer (OR =3.9, 95% CI = 1.9-8.0) and for drinking bottled water (OR= 8.6, 95% CI= 1.9-39.5). Other food items had no significant OR. Stratified analysis of exposure to za'atar fata'yer and getting sick in different grades showed a significant OR for students of the sixth grade only (OR = 6.2, 95% CI= 2.36-16.11). Further analysis of exposure to the bottled water failed to procure any real association. All the stool samples collected from the cases and one gastric lavage sample were negative for Food Borne Disease (FBD) pathogens. One za'atar fateera sent for toxicological and microbiological testing on the same day of incident was considered safe for human consumption. Food and drinks items collected from the school canteen the day following the incident and sent for both toxicological and microbiological testing were also safe. Throat swab, nasal swab, rectal swab and nail samples taken from the school canteen seller were negative. Some of the swabs of the bakery workers had grown staphylococcus aureus and E. coli. Fata'yer samples collected from the bakery had grown staph. aureus and E. coli as well.

On inspection of the school canteen and the canteen supplier warehouse, they were found to be unsuitable for storing food. The canteen sells za'atar and cheese fata'yer (baked dough pies filled with za'atar herb or cheese), in addition to long-life juices, milk, potato chips, biscuits and mineral water bottles. The za'atar and cheese fata'yer are brought to the school canteen on a daily basis at about 8:15 am and kept in plastic baskets in the canteen. Other items are stored in the canteen and supplied periodically. The canteen seller had a valid health certificate, no current hand wounds or blisters but he had long fingernails and was not wearing a uniform. On inspection of the za'atar and cheese fata'yer, they were singly wrapped in a plastic wrap that had no labeling. Some had no written expiry date and some plastic wraps were open. The canteen supplier actually buys the fata'yer from another local bakery. He picks them up at 6:00 am in plastic baskets and distributes them to the schools using poorly air-conditioned trucks, that reach the school where the outbreak occurred last, at about 8:15 am. The supplier claimed that left over fata'yer were distributed to the social society. No other schools supplied by the same supplier had reported a similar incident.

The bakery that bakes the fata'yer was located in Dammam, with 30 workers and a supervisor. All had valid health certificates. Some of the workers were not wearing either head cover or gloves, none had any skin lesion, and they denied any history of gastrointestinal symptoms. They start preparation of the Fata'yer at midnight by mixing the wheat flour with milk powder, yeast, water, oil, eggs, sugar and salt in a large stainless-steel bowel of the mixing machine. When the dough is ready it is left to rise for 1.5 €” 2 hours, then it is cut into small pieces by another machine and left to relax for another 1/2 hour, after which the dough is filled manually with the desired filling (cheese, za'atar and olive oil mixture). The Fata'yer are then baked in a hot oven for 10-15 minutes, after which they are singly wrapped in a plastic wrap and put in large plastic baskets, ready for the dealer to pick up at around 6:00 in the morning.

The short incubation period of mostly upper gastrointestinal symptoms reported in this outbreak suggests food borne intoxication rather than food borne infection. Food Borne Intoxication can be caused by certain bacteria, which under favorable growth conditions produce enterotoxins in food before it is consumed. The most commonly implicated microorganisms include Staphylococcus aureus, Bacillus cereus, Clostridium perfringens, and Vibrio parahaemolyticus. It generally takes less than 8 hours for these organisms to elaborate enough toxins to cause symptoms. The disease is characterized by an abrupt onset of symptoms of severe nausea, vomiting, diarrhea, and prostration with little or no fever.[1]

In this outbreak, the three possible causes to be considered are: Staph. aureus enterotoxins, Bacillus cereus vomiting enterotoxins, or chemical poisoning. Za'atar fata'yer is the most probable implicated food item. Contamination with any of these agents could have occurred at any stage of fata'yer production; starting from the raw material along the processing and handling line, up to transport and storage before selling to the consumers. Powder milk contaminated with Staph. aureus entertoxins is well documented to cause wide spread outbreaks.[2,3] Staph. aureus from the food handler could have contaminated the dough and produced toxins when given sufficient time.[2,3] Pesticides and Bacillus cereus spores €” which are widely available in the environment €”could have contaminated either the wheat flour or za'atar herbs. With water and appropriate temperature and time, available in the dough, the spores germinate and the bacteria multiplies, producing its toxins.[4] Both Bacillus cereus and Staph. aureus enterotoxins are heat stable and would not have been destroyed by baking of the fata'yer. However, this scenario is less likely to be true in the current outbreak, because it would have caused a much larger outbreak involving more than one school. The most likely scenario is that the baked dough was contaminated by Staph. aureus from the food handlers during wrapping, or that Bacillus cereus spores passed the baking oven safely. With appropriate temperature and time these organisms produced their toxins. Although the association was not causal, most likely Staph. aureus enterotoxins were the causative agent of that outbreak, za'atar fatayer served in the school canteen was the most probable implicated food. Contamination from food handlers and poor storage and transportation method are the most likely contributing factors.

A possible explanation to why only this school was affected and why sixth grade student in particular, may be that an infected bakery worker with toxogenic strain of Staph. aureus wrapped the za'atar fata'yer which was brought to this school, the last to receive the fata'yer, with a poorly air-conditioned truck after two and a half hours, and another 45 minutes in the poor environment of the school canteen, Staph. aureus produced their enterotoxins in the za'atar fata'yer which were mainly consumed by the sixth grade students who usually go to the break in one group and buy the food earlier than the younger students. Unfortunately, this explanation could not be proved.

Staphylococcal food intoxication usually follows ingestion of starchy food, meat, and poultry products. Other foods commonly involved are canned or potted meat or fish, pressed tongue, beef, cheese, other milk products, cream or custard filled pastries, potato salad, and pasta salads.[2,3] However, to confirm Staph. Aureus, the same phage type needs to be isolated from the stool or vomitus of two or more ill persons, or enterotoxin detected or 105 organisms/g isolated from the epidemiologically implicated food item, provided that the specimen is properly handled.[2,3]

In Saudi Arabia, the most common causative agent for FBDOs is Staph. aureus intoxication followed by Salmonellas. Contamination of food by food-handlers is the major contributing factor, followed by poor storage and non-safe-source food.[5]

It was recommended to compose an internal inspection team at the school to supervise the canteen and the supplier using a special form to be sent weekly to the preventive office, correction of the school canteen environment, application of HACCP (Hazard Analysis Critical Control Point Evaluation) in the inspection of the food safety in the food industry rather than depending on the final product analysis. A laboratory-based and an epidemiologically-based surveillance system covering outbreaks, sporadic cases and monitoring food contamination is a requisite for effective control of FBD which requires knowledge about food borne hazards, the current level of FBD in the country and the burden it places on the public health and the economy.