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


On July 31, 2018, Hail's food safety program reported an unexpected number of gastrointestinal illnesses had presented to Al-Shenan General Hospital. Patients reported a similar history of eating breakfast at the same restaurant. Objectives: To confirm the existence of the outbreak, confirm the diagnosis, define and identify the cases, identify the source of the outbreak, determine the causative agent or organism if possible and it's mode of transmission, and recommend preventive measures to be applied in order to prevent similar outbreaks in the future.


A 1:1 case control study was conducted to identify the source of the outbreak. Cases were defined as persons who ate food from Albait alhomsy restaurant in Al-Shenan town on Tuesday 31 July 2018 and developed gastrointestinal illness. Controls were persons who ate food from the same restaurant 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.


We interviewed 87/104 cases (83.7%): 5 cases were hospitalized and no deaths occurred. Cases were 41% male. The median age of cases was 27 years (range: 3-70 years). 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 (17.9%) were salmonella positive. Widal testing on the food handlers was positive Salmonella paratyphi for 4/6 (66%). Cases (98%) were significantly more likely to report eating falafel than controls (81.6 %) (OR=9.6, P VALUE 0.0004); cases (98%) were also significantly more likely to report eating hummus than controls (73.6 %) (OR=15.3, P VALUE 0.000003). Laboratory testing isolated Salmonella spp. from both items.


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 a higher level of supervision and periodic examination for food handlers.