Staphylococcus aureus Food Poisoning Outbreak in Al-Madinah Al-Monawarah, March 2003

On Saturday 1st March 2003, a large number of Iranian Hajjis presented to several hospitals in Al Madinah Al-Monawarah; King Fahad hospital, Al Ansar, Al Miqat, Ahud hospital, other private hospitals in addition to the Iranian Medical mission. They were complaining of vomiting, nausea, abdominal pain and diarrhea after eating food prepared in the kitchen of their Hamla's food supplier. All the patients gave history of eating food prepared by "Al-Dakheel Catering" in Al-Madinah. A team from the Field Epidemiology Training program (FETP) was assigned to investigate this outbreak. The aim of this study was to determine the size, severity and extent of the outbreak, to determine its source, and to place recommendations that may prevent similar outbreaks in future.

Medical records of the affected individuals in the hospitals and the Iranian medical mission were reviewed. A questionnaire was developed and translated to Persian. It covered demographic information, signs and symptoms, time of symptom development, treatment, whether admitted into hospital and date, of discharge if admitted, type of food eaten, date and time of eating the food, and amount. Laboratory results of samples collected from patients and kitchen workers' including samples from vomitus, rectal, throat and nasal swabs, stool, and specimens from the remnant food were obtained. There were 492 cases identified.

A case control study was conducted. A case was defined as any person who ate lunch food supplied by "Al-Dakheel Catering" on Saturday March 1, 2003 and developed one or more of the following symptoms: nausea, vomiting, abdominal pain, and diarrhea. It was not possible to interview all the Iranian Hajjis who ate from that lunch food on Saturday, March 1, 2003, since many had already left back to their country. Therefore not all the cases reported were interviewed. It was possible to identify a number of Hajjis who had eaten from the same kitchen on the same day and had not complained of any symptoms, and these were considered controls. A case to control ratio of 1:1 was chosen.

A total of 414 persons were interviewed, 207 cases and 207 controls. All cases were Iranian, with ages ranging from 25-81 years; 122 (58.9%) were males. From the total number of the cases, 197 (95%) complained of vomiting, 163 (78.7%) abdominal pain, 156 (75.4%) nausea, and 56 (27%) diarrhea. Four food items were eaten: Rice (Attack rate (AR) 99.5%, Odd's Ratio (OR) 10506), Chicken (AR 99.5%, OR 00), Bread (AR 2.4%, OR 0), and Yoghurt (AR 17.4%, OR 0). Only 13 (6.3%) cases were admitted to hospital. All remaining cases had received treatment at the accident and emergency departments, and recovered from symptoms within 24 hours.

It was not possible to interview the chefs or the assistants since they had already left. However, according to one of the kitchen administrators, preparation of the lunch food went through several steps. The kitchen workers took out the frozen chicken at 4:00 pm the previous afternoon and left it to thaw until 10:00 pm. After that, they cut it and kept in refrigerators. Actual cooking of the rice and chicken began at 1:00 am. The process of cooking ends at 'about 5:00 am. At 6:00 am the cooked food is placed in special heaters, each with a capacity of 290-300 meals, which are trans-ported in special trucks to the hotels where the Hajjis are staying. The kitchen is about 4 km away from the hotels. Each Hamla leader receives one heater according to the number of Hajjis in his group. The heater is connected to the electricity to maintain a temperature of 80°C. The group leader and his assistants serve the lunch at 1:00 pm. The bread and yoghurt are supplied from the local market. That day, the kitchen prepared lunch for 9600 hajjis.

The outbreak started on the evening of Saturday March 1, 2003. The time interval between food consumption and appearance of symptoms ranged from 3 to 7 hours with a median of 4 hours. The rice and the chicken were the implicated food items (OR 10506 and co respectively, P value < 0.005).

Staphylococcus aureus was isolated

from the nasal and throat swabs of two workers and from the stool cultures of 13 of the workers responsible for food preparation. It was also isolated from the vomitus of 10 cases. The bacteria was also found in the food remnants specimens (23 specimens from the chicken and 9 from the rice) taken in the hotels when the outbreak started. Serotyping of the bacteria was not done.

Bacterial food poisoning results from consuming food contaminated with bacteria or its toxins. Two types of bacterial food poisoning are recognized; the infective type, which results from ingestion of food contaminated with large numbers of bacteria; and the toxic type, which results from ingestion of food contaminated with preformed toxins.[1]

Staphylococcal food poisoning is caused by ingestion of food that contains preformed toxins.[1] Staphylococcus aureus are gram-positive cocci, that grow in clusters, aerobically and anaerobically, at an optimum temperature of 37°C, and are readily killed by temperature above 55°C. People may harbor the organism either persistently or intermittently, and about 25% of populations are carriers. Foods are easily contaminated by staphylococci from infected skin and other septic lesions such as boils, cuts and burns. Cold foods, much handled during preparation, are the most common vehicles of infection.[2] The enterotoxin is produced in food before it is consumed, hence the incubation period is very short (30 minutes to 8 hours), usually 2-4 hours after consuming contaminated food.3 Epidemics of food borne staphylococcal gastroenteritis occur worldwide. The highest incidence is in areas where personal hygiene is suboptimal and people are crowded.[3]

Epidemiological evidence in this investigation showed that chicken and rice was the most likely vehicle of transmission and staph. aureus caused this outbreak. The symptoms and their time of onset are consistent with staph. aureus outbreaks.[4] Improper food-handling practices contributed to the development of this outbreak.

It was recommended that workers who handle food must be trained on safe food preparation practices before issuance of the health certificate from the concerned authorities, supervisory personnel should be educated on the need to monitor food handlers for skin lesions and sources of contamination.