On July 23, 1998, an outbreak of food poisoning occurred among the residents and workers of a Social Rehabilitation Center (SRC), Madinah, Saudi Arabia. The objectives of this study are to assess the extent of the outbreak, to identify its source, and to suggest recommendations that would prevent occurrence of similar outbreaks in the future.
Methodology
All members of the community at the SRC were interviewed whether or not they experienced any of the symptoms of food poisoning. Details were collected on preparation of food and drink. Stool specimens and rectal swabs were taken from 27 patients admitted to hospitals.
Results
Among 379 persons who usually take meals at the SRC, 125 were identified as cases of food poisoning (Attack Rate [AR] = 33%). Although all meals were prepared in the same kitchen (male section), the AR among those served by workers in the male section was 84.5%, whereas there were no cases among those served by female workers in the female section (AR = 0.0 %). Of all 9 meals served during the 3-day period prior to symptom onset, the outbreak was associated with watermelon served at lunch on 23/07/98 (AR = 42.8%). In the male section, 148 persons took some watermelon and 125 (84.5%) had symptoms of food poisoning. Of those, 122 (84.1%) took watermelon as a drink and 3 took watermelon as slices. Salmonella enterica serogroup enteritidis was isolated from 21 patients. The median incubation periods of those having watermelon drink and slices were 8 and 12 hours respectively. Both the knife and cutting board in the male section were used to slice the watermelon and had been used to cut more than 120 raw chickens served the day before the outbreak. The sliced watermelon drink was kept at room temperature for at least 2 hours before blending at mid-day.
Conclusion
This outbreak documents an uncommon vehicle for salmonellosis: watermelon. It is most likely that watermelons were contaminated while they were sliced on a dirty cutting board. Being kept at room temperature in an already warm kitchen probably favored overgrowth of bacteria. The blending of watermelon could explain the high AR observed in this study.