The first outbreak of E. coli O103 caused by raw chopped celery under review


E. coli O103, one of the rarest shigatoxin-producing E. coli, sickened patients at two hospitals in Victoria, British Columbia, last April. The Vancouver Island outbreak is now the subject of a food safety review for high-risk products prepared for vulnerable populations.

Based on confirmed cases of E. coli O103 reported to Island Health’s Infectious Diseases Unit, whole genome sequencing was used in the case study. The Canada Communicable Disease Report (CCDR) published the study in its January 2022 edition.

The Victoria outbreak identified six confirmed cases of E. coli O103, of which 67% were women and had an average age of 61 years. All were inpatients or outpatients at both hospitals. All ate raw chopped celery sandwiches prepared by hospital food services.

There has been little product testing on celery, and residual E. coli contamination has occurred during the chopping process, and “temperature abuse” in hospitals is suspected to have contributed to the ‘epidemic.

The April 2021 outbreak of E. coli O103 was an unusual increase. Previous outbreaks of E. Coli O103 were linked to clover sprouts, bison meat, ground beef, mutton jerky, raw milk and fermented sausages.

Celery was previously reported as a vehicle for Listeria monocytogenes, norovirus, and E. coli O157:H7, but not O103. The objective of the CCDR study “is to describe the first outbreak of E. coli non O157 associated with celery in Canada and to identify safety concerns for high-risk products prepared for vulnerable populations, in order to reduce the likelihood of such outbreaks in the future. ”

The study authors were from the Public Health Agency of Canada, Island Health and BC Centers for Disease Control.

The report went on to say:

“All cases had been admitted to or visited two Victoria area hospitals during their exposure period. Of the six confirmed cases, four were admitted to Hospital A, one was admitted to Hospital B, and one case was not admitted to hospital but went to the hospital emergency room.

The study found no related cases identified in the same period as the nationwide Victoria outbreak in Canada or the United States.

Discussion and discovery
“This investigation resulted in several recommendations to improve the food safety of this food in the health region of the island,” according to the report. “Evidence from epidemiological and food safety investigations confirms that chopped celery is the source of this outbreak. All six confirmed cases were exposed to the suspected source and no other products were reported in the six confirmed cases, despite detailed menus for all hospitalized patients. An outpatient who only ate a tuna and celery sandwich during his visit to the emergency room at Hospital A, the outlier case added further support for celery as a suspect source.

“This investigation also revealed strong traceback evidence – the chopped celery served at Hospital A and Hospital B was supplied by the same supplier; the investigation also revealed strong evidence of traceability – the supplier only supplied the chopped celery product to the two hospitals, and nowhere else. Since the contaminated product was no longer available at the time of the investigation and due to the cleaning procedures of Transformer A, neither the product samples nor the environmental samples were available for testing. Despite the lack of laboratory evidence, the authors believe that the strong epidemiological, traceback, and traceback evidence is sufficient to implicate chopped celery in this outbreak.

“The outbreak highlights the risk of raw vegetables supplied to vulnerable populations and draws particular attention to the risk of chopping during processing. Although previous work has documented the potential food safety hazards of fresh produce this outbreak serves to document the potential risks posed by hashing, which allows small amounts of bacteria remaining on the surface of a product, even after chlorination, to spread throughout an entire batch. The attribution of the chopping step as problematic in this outbreak scenario is further supported by the fact that a traceability investigation revealed that coarser chopped celery from the same batch was supplied to an extensive distribution network. , excluding Hospital A and Hospital B, with no outbreak cases. strain of E.coli O103 associated with this product.

“Despite providing food to a population of approximately 800 hospitalized patients each day, the identification of only six cases in Hospital A and Hospital B could potentially be explained by a low level of contamination, which may n have caused disease only in those whose sandwiches were subjected to temperature abuse. Temperature abuse is a known vector for the spread of pathogens and was reported by hospitals during follow-up to the survey. It is assumed that any contamination present after the chopping stage in Processor A was further spread by these reports of temperature abuse, resulting in the reported illnesses. A recommendation was made to the two hospitals involved to add a time stamp to all sandwiches to mark the time the product was taken out of the refrigerator, to reduce the risk of temperature abuse in the future.

“There are several limitations to consider when interpreting these outbreak data. First, exposure data for celery were not available for healthy population controls to directly compare. outbreak cases However, given that 100% of confirmed cases were exposed to the suspected source, and this was the only common exposure in all six cases, the authors are confident in the epidemiological evidence of this product. Second, the reporting time for this outbreak was long, which delayed the identification and investigation of the outbreak. Reporting times are influenced by a multitude of factors, but comorbidities among hospitalized cases and outpatients in this outbreak may have delayed the review of an enteric illness diagnosis and thus the request for a stool specimen for testing.Third, several cases lacked onset dates because there s could not be queried. For these individuals, their date of onset is likely to be earlier than their sample collection date, which would also affect their exposure period. This was taken into account when interpreting exposure data and analyzing hospital menus. Fourth, there were no food samples available to test for the presence of E.coli O103; therefore, there were no laboratory data to definitively confirm the source of this outbreak. However, despite the lack of laboratory confirmation, the authors believe that epidemiological evidence, traceback data, and traceback data strongly supported the suspect source. Finally, it was not possible to determine where or how E. coli was introduced, as additional follow-up at the producer in the United States was outside the jurisdiction of the investigation of this outbreak.

Conclusion of the study
“Raw vegetables, such as celery, are a known source of E.coli contamination and pose a risk to vulnerable populations. Mincing during raw vegetable processing and temperature abuse prior to consumption may provide additional levels of risk,” according to the report.

“This outbreak has prompted several recommendations to reduce the risk of chopped celery served in hospitals, including more frequent testing at the processor, a review of the chlorination and chopping process, and a review of hospital food service practices to reduce temperature abuse.

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