Outbreak investigation of Salmonella: Aleshenan province, Hail, Saudi Arabia, 2018. A case-control study

  • Water or foodborne
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Background:
On July 31st, 2018, Hail city reported an unexpected number of gastrointestinal illnesses had presented to Alshenan General Hospital. Patients reported a similar history of eating breakfast at the same restaurant. In Saudi Arabia, foodborne illness represents a major public health issue with more than 2,000 documented cases of foodborne illness in 2016. The objectives of the investigation were to determine the source of infection and the causative agent.

Methods:
We conducted a case-control study to identify the source of the outbreak. We defined cases as persons who ate food from Restaurant A in Alshenan province on Tuesday 31 July 2018 and developed gastrointestinal illness. Controls were persons who ate food from Restaurant A without reporting symptoms. We collected information on demographics, symptoms, and food history using a semi-structured questionnaire. We reviewed hospital records for symptoms and clinical course. We reviewed available laboratory results for cases, food handlers, and environmental samples.

Results:
We interviewed 87/104 cases (83.7%): 5 cases were hospitalized and no deaths occurred. The median age of cases was 27 years (range: 3-70 years), and 41% were male. All cases reported diarrhea, other reported symptoms included abdominal cramps (98%), fever (94%), headache (85%) and vomiting (71%). The incubation period ranged from 8-52 hours. Out of 56 rectal swabs from cases, 10 (18%) were Salmonella spp. positive. Widal testing on the food handlers was positive for Salmonella paratyphi for 4/6 (66%). Cases (98%) were significantly more likely to report eating falafel than controls (82%) (OR=9.6, P VALUE 0.00); cases (98%) were also significantly more likely to report eating hummus than controls (74 %) (OR=15.3, P VALUE 0.00). Laboratory testing isolated Salmonella spp. from both items.

Conclusion:
Based on symptoms, incubation period, the epidemiological investigation, and laboratory results, this outbreak was most likely caused by Salmonella spp. contamination of falafel and/or hummus. These food items were served together and share common ingredients; we were unable to more definitively identify the source of the outbreak. We recommend additional training on safe food preparation and routine examinations of restaurants and food preparation practices.

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