In June 1992, 19 cases of suspected typhoid fever were reported from the town of Al-Mudhnab (population 10,000) in the Qassim region. The median number of cases in the entire region for the last four years was four; there were two cases in Al-Mudhnab in the first five months of 1992. The objectives of this study were to find all possible typhoid cases, to identify the mode of transmission, and to determine corrective or preventive measures.
Methodology
We reviewed the laboratory logbook, hospital admission and discharge records, primary health care center referral logbooks and records of school clinics. We reviewed the medical records of 27 cases (suspected and confirmed typhoid). We defined suspected typhoid as a high Widal test for Salmonella typhi O antigen but negative blood, stool and urine results and confirmed typhoid as suspected typhoid with S. typhi isolated from blood, stool or urine. We reviewed bacteriology and chlorination records of the town water supply. We identified the location of food sources, such as groceries and cafeterias, in the cases' neighborhoods. We developed a questionnaire that encompassed school and other activities and food eaten outside the home. We interviewed the typhoid fever patients at their homes. We selected 55 control persons of the same age and sex from randomly selected houses in the same neighborhood.
Results
We identified 17 bacteriologically confirmed cases of typhoid fever with onset from May to July. Ten of the cases were females (53%), and these clustered by onset in a 15-day period. Cases in males followed the girls and were more dispersed. Cases included 12 school-age children, four preschool children, and the wife of a girls' school bus driver. The attack rates (AR) did not differ between boys' and girls' schools and ranged from 2.8 to 3.8 per 1,000 in six different schools. All patients except one lived within two blocks in one quarter of the town. Typhoid fever was associated with attending or eating food prepared for a school potluck dinner (OR = 8; 95% CI 1.5-44). There were two other potluck dinners on the same night and children had trouble remembering what they had eaten. Cake with cream topping from one dinner was kept overnight at room temperature and served to girls on the bus the next day. The OR of eating cake on the bus and becoming ill was 12 (95% CI 1.7-106).
Conclusion
The localization of this outbreak by time and place and the age groups affected supports the conclusion that the outbreak was foodborne. The most likely food was cream topping for cake. Lessons on proper food handling and storage should be included in home economics classes.