ARCHIVED - Restaurant foodhandler-associated outbreak of Salmonella Heidelberg gastroenteritis identified by calls to a local telehealth service, Edmonton, Alberta, 2004
On 22 June, 2004, Capital Health-Public Health Division (the local public health department for the metro Edmonton, Alberta, region) received multiple reports of gastrointestinal illness among individuals who had consumed a meal, some hours before onset, at an Edmonton buffet-style restaurant specializing in South Asian cuisine. The initial reports of illness linked to the restaurant were received through two separate telephone calls to a local telehealth service (Capital Health Link). Transcripts of the telehealth calls were forwarded to the local public health department and resulted in the initiation of an outbreak investigation.
The individuals named in the initial reports had laboratory-confirmed Salmonella in stool specimens. All laboratory-confirmed cases of Salmonella gastroenteritis identified in residents of the Capital Health region are reported to Capital Health's Medical Officer of Health (MOH), as per the requirements of the Public Health Act. Such cases are contacted by Environmental Health Officers (EHOs) on behalf of the MOH to administer an exposure questionnaire for disease surveillance purposes. While possible associations with other exposures were also investigated, additional Salmonella cases (and others in the same dining party) linked to the implicated restaurant were asked detailed questions by EHOs regarding the clinical presentation of their illness and foods consumed at the restaurant.
All Salmonella cases identified in Alberta are subject to serotyping by the Alberta Provincial Laboratory for Public Health (PLPH) (Microbiology). Pulsed field gel electrophoresis (PFGE) analysis was performed at the request of Capital Health upon identification of the Salmonella cluster. A Salmonella cluster PFGE pattern was identified and included in the case definition after confirmation of the pattern with a second restriction enzyme.
Two additional methods of case finding were used. An alert regarding the outbreak was posted on a secure Public Health Agency of Canada (formerly Health Canada) administered web-based surveillance information system (Canadian Enteric Outbreak Surveillance Centre, or CEOSC) accessed by local, provincial and federal epidemiologists. The Salmonella PFGE cluster pattern was also posted on two laboratory-based surveillance information systems (PulseNet Canada, CDC PulseNet).
On and after 22 June, 2004, EHOs visited the implicated restaurant to conduct inspections and interview restaurant management regarding food handling practices. Employees were asked to submit stool specimens for Salmonella screening; these specimens were collected on 24 and 25 June, 2004, and submitted to PLPH for analysis. Additional reports of illness linked to the restaurant were received by the local telehealth service, the regional pediatric hospital and the emergency department of an Edmonton hospital during the course of the outbreak, and these were forwarded to the local public health department for investigation.
The case definition for this outbreak was restricted to residents of or visitors to the Capital Health region (metro Edmonton, Alberta) with Salmonella Heidelberg of a PFGE pattern indistinguishable from pattern SheXAI 0.0001 (national designation) isolated in a clinical specimen collected on or between 1 June and 15 July, 2004. A total of 32 cases of this Salmonella Heidelberg type were identified in the region during the outbreak period, one of whom was an employee of the implicated restaurant. One case lived in Alberta but outside the Capital Health region, and one case resided in another Canadian province. The mean and median age of cases was 26 and 29 years respectively, with a range of 10 months to 59 years. Thirteen individuals who were in the same dining party as an outbreak case and reported gastrointestinal illness following the meal were also interviewed, but these were not counted as cases for the purposes of this investigation if there was not a laboratory-confirmed Salmonella Heidelberg case of the outbreak type.
Reported symptoms among outbreak cases included diarrhea (100%), fever (93%), abdominal cramps (85%), nausea (82%), vomiting (59%), body ache (59%) and bloody diarrhea (19%). Six cases (19%) were reportedly hospitalized as a result of their illness, and, of these, three were < 5 years old at onset. Illness onset dates ranged between 15 and 30 June, 2 2004 (Figure 1). The mean duration of illness was 7.4 days. One case was asymptomatic.
Twenty-seven of 31 outbreak cases (87%), excluding the infected employee, reported consumption of food at the restaurant during the approximately 72 hours before they became ill (i.e. within the incubation period for Salmonella infection(1)). Incubation periods (i.e. time between implicated meal consumption and onset of illness) ranged between 7 and 74 hours, with a mean and median of 22 and 16 hours respectively. No food-specific associations (for any one buffet item or ingredient) could be elucidated from the exposure histories. The dates when outbreak cases had eaten at the implicated restaurant ranged between 15 and 25 June, 2004.
Employee stool sample results
Stool specimens were collected from five employees of the implicated restaurant. The specimen of one employee was positive for Salmonella Heidelberg, which was of the outbreak type.
Inspection findings and interviews with restaurant staff
No improper food handling practices were noted at the restaurant during the investigation. New batches of each menu item were reportedly prepared each day. An EHO interviewed staff in their first language (Punjabi); none (including the Salmonella-infected employee) indicated that they had been ill with diarrhea in the previous few weeks. It was confirmed that the foodhandler infected with Salmonella was involved in foodhandling activities as part of normal duties.
Public health measures
On 29 June, 2004 (the day that the Environmental Public Health Services received the positive laboratory result), the MOH excluded the restaurant employee found to be positive for Salmonella from occupations involving food handling, pending two consecutive negative samples. EHOs visited the implicated restaurant on several occasions during the outbreak period to ensure that the excluded employee was not working and to ensure that safe foodhandling practices were being used.
This investigation confirms that an outbreak of infection with Salmonella Heidelberg (of a PFGE pattern indistinguishable from SheXAI 0.0001) occurred in the Capital Health region in June 2004, as 32 cases of this particular type occurred in residents of or visitors to the region during a relatively short time. There is strong epidemiologic evidence to suggest that food served at an Edmonton restaurant was the source of the outbreak: most cases had had this exposure during the incubation period for Salmonella infection, and no other significant epidemiologic link was identified among cases. The ultimate cause of the outbreak was not confirmed. However, information collected during the investigation is consistent with the outbreak occurring as a result of contamination of food by a Salmonella-infected restaurant employee.
Isolation of the same specific Salmonella subtype from the infected restaurant employee and restaurant patrons, the fact that implicated meals were consumed over a 10-day period (when food served at the restaurant was prepared fresh daily) and the lack of a food-specific association with illness is also consistent with the employee contamination hypothesis. It was confirmed that the Salmonella-infected restaurant employee was shedding the pathogen on June 24 (the day the positive stool sample was collected), and it is probable that this individual was shedding Salmonella bacteria during the entire 10-day period during which outbreak cases consumed their implicated meal. Those infected with Salmonella typically have onset of gastroenteritis as a result; they shed the pathogen in stool while symptomatic and for an average of 4 to 5 weeks, and sometimes several months, after resolution of symptoms(2). It is of note that no cases reportedly consumed their implicated meal after the Salmonella-infected restaurant employee had been excluded, on June 29. This is also consistent with the infected employee being the reservoir of the infection, as removal of this reservoir coincided with the end of the outbreak.
Salmonella infection is spread through the fecal-oral route, with food being the usual transmission vehicle(2). Salmonella-infected foodhandlers are frequently documented as the reservoir in foodborne Salmonella outbreaks(3-5). It has long been known that Salmonella bacteria survive on the fingertips for several hours and that food can be contaminated through contact with fingertips inoculated with < 100 organisms(6). Thus, slight breaches in hand hygiene by those infected, resulting in even microscopic fecal contamination of fingertips, could result in such an outbreak.
PFGE analysis was used to develop a stringent case definition for this outbreak. Human Salmonella Heidelberg isolates identified in the Capital Health region during the outbreak period that were not of the outbreak pattern could be excluded from the analysis, thus strengthening the exposure association. The PFGE analysis was also used to identify Salmonella Heidelberg outbreak cases outside of the Capital Health region, cases that may not have otherwise been epidemiologically linked. The utility of PFGE analysis as an epidemiologic tool in the surveillance of enteric pathogens such as Salmonella and Escherichia coli O157:H7 has been repeatedly demonstrated(7).
Enteric infection surveillance in the Capital Health region makes use of information from several sources, of which the most recently tapped is a local telehealth service. Capital Health Link is a telephone health advice service answered by registered nurses and available 24 hours a day, 7 days a week, to anyone in the Capital Health region. A process has been developed through which suspected foodborne illness reports received by the telehealth service are immediately forwarded to the local public health department for investigation, and this assisted in the early identification of this outbreak. The benefit of a linkage between telehealth services and public health departments for disease surveillance in Canada, described elsewhere(8), was realized in this investigation.
The authors thank the following for their assistance: S Letourneau, Capital Health Link, Edmonton, Alberta; S Sihota, Health Canada, Alberta/Northwest Territories Region, Edmonton, Alberta; and S Tawfik, Capital Health-Public Health Division, Edmonton, Alberta.
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Source: L Honish, BSc, N Hislop, BSc, I Zazulak, CPHI(C), Capital Health-Public Health Division, Edmonton, Alberta; L Chui, MSc, G Tyrrell, PhD, Provincial Laboratory for Public Health (Microbiology), Edmonton, Alberta.
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