Article Info
Authors
Dr. Nasser Al-Sheik
Year: 2001
Month: July
Issue: 3
Reference: Alsaedi T., AlGheilani A., Turkistani AM., Nooh R., Alsulaiman M.,Dr. Nasser Al-Sheik .Saudi Epidemiology Bulletin. 2001;8(3):.
On July 1st, 2000, an outbreak of food poisoning occurred among attendees of two wedding parties in Riyadh city, both served by the same restaurant. A team from the Field Epidemiology Training Program investigated this outbreak. A retrospective cohort study was conducted. A case was de-fined as any person who ate at party A or B, on July 1st 2000, and developed diarrhea within 3 days.
We attempted to interview all the attendees of both parties whether they had become sick or not. The discharge summaries and laboratory investigations of those who were admitted to hospitals were reviewed. The restaurant was visited, and a list of food items and details of food preparation techniques were obtained.
The dinner meal was served around 11:00 p.m. on July 1st, and symptoms started to appear 5 hours up to 53 hours later. The median incubation period for both parties was 15 hours and the epidemic curve suggested a common source outbreak.
We were able to interview 160 cases (134 from party A and 26 from party B) and 123 controls (110 from party A and 13 from party B). Among patients of party A, 74 (55.2%) were males and 60 (44.8%) were females (1.2:1 male to female ratio). Among patients of party B, 23 (88.5 %) were males and 3 (11.5 %) were females (7.7:1 male to female ratio). All the patients were Sudanese with a median age of 28 years (Range 1-60).
At party A, out of 134 attendees who had become sick, 15 (11.2%) had been hospitalized. The most common symptoms were diarrhea (100%), colicky abdominal pain (94.4%), and fever (91.3%). Out of 15 food items served, 8 were significantly associated with the illness (Table 1). At party B, among 26 who had become sick, only one (3.8%) had been hospitalized. The median duration of diarrhea was three days and that of vomiting was one day. Mayonnaise salad was the only food item served at both parties that was significantly associated with the outbreak (RR=11, 95% CI = 1.7-71.3) (Table 1).
A total of 48 patients had a positive stool culture for Salmonella group B non-typhi and 10 others for Salmonella of unidentified group. Out of 7 restaurant workers, two (28.6%) were found to have Salmonella group B in their rectal swab, but with no history of diarrhea.
Preparation of the mayonnaise salad involved peeling and slicing potatoes with bare hands, then mixing them with thawed commercial vegetables. The mixture was boiled for 15 minutes then kept at room temperature for over 30 minutes until it cooled down. After that, commercial mayonnaise was added to the vegetable salad in stainless steel jars, mixed well, and kept at room temperature (35-40°C) a median of five hours before serving. At both parties, a restaurant worker served the meal to each guest.
Editorial note:
The results point to the mayonnaise salad as the most likely food item responsible for this outbreak. Several reported outbreaks due to Salmonella species have implicated salad as the vehicle for transmission. [1-3] Other food items associated with the outbreak in party A was most probably due to cross-contamination.
The source of the outbreak was probably an asymptomatic food handler, who have been identified as sources of Salmonella infection in many outbreaks.[4-5] Salmonella can survive on fingertips for at least 3 hours. Inoculates of less than 100 organisms per finger can lead to contamination of 90% of handled food.[5]
Among the ingredients of the mayonnaise salad, potato was most likely the initially contaminated ingredient. However, it is known that when food is contaminated with fecal bacteria from hands, the contamination level is usually very low, and a serious hazard only arises if the bacteria are allowed to multiply to harmful numbers under adverse storage conditions.[6] In this outbreak, time-temperature abuse and inadequate heat treatment were the main factors in producing this explosive outbreak.
Although the restaurant claimed using commercial mayonnaise, local preparation of mayonnaise using raw eggs is a widespread practice. During the past 10 years, 12 other studies were conducted by the FETP investigating outbreaks of Salmonellosis, 6 of which have incriminated the use of raw eggs and restaurant-prepared mayonnaise as the vehicle of transmission. Time-temperature abuse and poor temperature control in storing eggs (in both markets and homes) also contribute to infection.
It is extremely important that restaurants only use commercial mayonnaise. It is also advisable that restaurants use only pasteurized eggs for preparation of food items that require raw eggs as an ingredient. All restaurants should be subject to standards of safety in food preparation with emphasis on avoidance of cross-contamination and time-temperature abuse. Promotion of health education to food handlers is recommended, along with application of hazard analysis critical control point to routine inspection of restaurants. Salmonella excretory should not handle food until their stool cultures have proved negative for at least 3 times. Public awareness should be raised regarding the high risk of Salmonellosis when raw eggs are used in cooking.
References
- Maguire H, Pharoah P, Walsh B, Davison C, Barrie D, Threlfall EJ, Chambers S. Hospital outbreak of Salmonella virchow possibly associated with food handler.J Hosp Infect 2000; 44 (4): 261-6.
- Blaser MJ, Rafuse EM, Wells JG, Pollard RA, Feldman RA. An outbreak of salmonellosis involving multiple vehicles. Am J Epidemiol 1981; 114 (5): 663-70.
- Torok TJ, Tauxe RV, Wise RP, Livegood JR, Sokolow R, Mauvais S, Birkness KA. A large community outbreak of Salmonellosis caused by intentional contamination of restaurant salad bars. JAMA 1997; 278 (5): 38995.
- Faustini A, Sangalli M, Fantasia M, et al. An outbreak of Salmonella hadar associated with food consumption at a building site canteen. Eur J Epidemiol 1998; 14 (1): 99-106.
- Heiberg CW, White KE, Jon-son JA, et al. An outbreak of Salmonella enteritidis infection at a fast food restaurant: Implications for foodhandler-associated transmission. J lnf Dis 1991; 164: 1135-1140.
- DE Wit JC, Rombouts FM. Fecal microorganisms on the hands of carriers: Escherichia coli as model for Salmonella. Zentralbl Hyg Umweltmed 1992; 193(3): 230-6.
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Table I: Attack rates for some food items during the food poisoning outbreak among attendees of two wedding parties, Riyadh, July 2000.
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Food items
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Party A
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Party B
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RR
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95 %CI
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P-value
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RR
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95 %CI
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P-value
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|
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Chicken
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1.44
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1.05-1.96
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0.007
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2.9
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0.89-9.46
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0.01
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Meat
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1.22
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1.0-1.49
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0.052
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1.43
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0.87-2.35
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0.14
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Sausage
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1.39
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1.l5-1.68
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0.001
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1.36
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0.89-2.08
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0.14
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Cheese
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1.27
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1.04-1.55
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0.02
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1.33
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0.68-2.60
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0.37
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Musaqa
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1.61
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1.40-1.85
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0.00
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1.3
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0.87-1.96
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0.27
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Pasta
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1.36
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1.1 0-1.67
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0.003
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1.19
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0.73-1.97
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0.45
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Bread
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1.34
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1.06-1.69
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0.008
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1.33
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0.68-2.60
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0.33
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Mayonnaise
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2.98
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2.17-4.10
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<0.001
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11
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1.7-71.3
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<0.001
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