Bacterial pathogens and indicators in seaweed salad – April 1, 2021, to March 31, 2024

Food microbiology – Targeted surveys – Final report

Bacterial pathogens and indicators in seaweed salad – April 1, 2021, to March 31, 2024 (PDF – 744 kb)

Summary

A targeted survey^Footnote 1 analysed 858 samples of seaweed salad over a 3-year period from April 1, 2021, to March 31, 2024, for the presence of the pathogens Listeria monocytogenes (L. monocytogenes), Salmonella species (spp.), and E. coli O157. All samples were also tested for generic E. coli which is an indicator of the hygienic and sanitary conditions of the food supply chain from production to the point of sale.

A majority (98.1%) of the samples tested were found to be satisfactory. Salmonella spp., E. coli O157, and generic E. coli at elevated levels were not detected in any of the samples. L. monocytogenes was found in 16 of the 858 (1.9%) samples, however these 16 samples (which were all frozen) represented only 5 unique lot codes of products. The frozen products sampled under this survey had shelf lives of up to 2-years and consequently some lots were sampled multiple times throughout the survey period. The Canadian Food Inspection Agency (CFIA) conducted appropriate follow-up activities. There were no reported illnesses related to these products.

Overall, our survey results indicate that seaweed salad sold in Canada is generally safe for consumption. However, as with all food, and especially those that are ready-to-eat (RTE) good hygienic practices are recommended for producers, retailers, and consumers.

Why the survey was conducted

The survey was conducted to generate baseline information on the quality and safety of seaweed salad sold at retail in Canada.

The consumption of seaweed has a long history in may parts of Europe and Asia^Footnote 2. However, in recent years it has grown in popularity in Western countries including Canada as people continue to embrace foods and flavours of cuisines from different parts of the world. Seaweed salad is generally made using wakame seaweed combined with a dressing consisting of a base of sesame seed oil, soy sauce, and vinegar. Unfortunately, seaweed has been associated with foodborne illness outbreaks^Footnote 3^Footnote 4^Footnote 5^Footnote 6.

Contamination with bacterial pathogens can occur at any step in the food supply chain such as during production, processing, packaging, distribution, at retail, and/or during preparation for consumption. Consequently, if pathogens are present, there is a potential for foodborne illness as seaweed salads are RTE.

When the survey was conducted

The survey was conducted over a 3-year period from April 1, 2021, to March 31, 2024.

Where the samples were collected from

Samples were collected from national retail chains and local/regional grocery stores located in the following 11 major cities across Canada:

Halifax
Moncton
Quebec City
Montreal
Toronto
Ottawa
Vancouver
Victoria
Calgary
Saskatoon
Winnipeg

The planned number of samples to be collected from each city was based on the population of the province in which the city was located relative to the total population of Canada.

Total number and description of samples collected

A total of 858 fresh and frozen seaweed salad samples were collected. A sample consisted of a single or multiple consumer sized packages of the same lot weighing at least 250g.

What the samples were tested for

All samples were tested for L. monocytogenes, Salmonella spp., E. coli O157, and generic E. coli. L. monocytogenes, Salmonella spp., and E. coli O157 are pathogenic bacteria while generic E. coli is an indicator of the overall hygienic and sanitary conditions under which the samples have been processed, stored, and transported.

Methods used to test the samples

Samples were analyzed using analytical methods published in Health Canada's Compendium of Analytical Methods for the Microbiological Analysis of Foods^Footnote 7 that were suitable for the testing of seaweed salad.

How were samples assessed

The samples were assessed using criteria based on the principles of the following Health Canada documents: Health Products and Food Branch (HPFB) Standards and Guidelines for Microbiological Safety of Foods – An Interpretive Summary^Footnote 8, Policy on Listeria monocytogenes in Ready-to-Eat Foods^Footnote 9 and the Food and Drugs Act^Footnote 10 (Section 4(1)).

Table 1 – Assessment criteria
Bacteria	Satisfactory	Investigative	Unsatisfactory
L. monocytogenes	Not detected	Not applicable (category 1^{Table Note a}) Detected and ≤10² Colony Forming Unit (CFU)/g (category 2^{Table Note a})	Detected (category 1^{Table Note a}) >10² CFU/g (category 2^{Table Note a})
Salmonella spp.	Not detected	Not applicable	Detected
E. coli O157	Not detected	Not applicable	Detected
Generic E. coli	≤ 10² Most Probable Number (MPN)/g	>10² MPN/g	Not applicable

No assessment guidelines had been established in Canada for the presence of Salmonella spp., E. coli O157, or generic E. coli in seaweed salad at the time of writing this report.

As Salmonella spp. and E. coli O157 are considered pathogenic to humans the presence of either organism might be considered a violation of the Food and Drugs Act^Footnote 10 Section 4(1)a and therefore assessed as unsatisfactory.

Unlike bacterial pathogens, most strains of generic E. coli are harmless. Generic E. coli is considered to be an indicator organism as their levels present in a food product are used to assess the overall sanitation conditions throughout the food chain from production to the point of sale. Their presence at some levels is tolerated, however elevated levels were assessed as investigative, possibly resulting in further follow-up actions.

Survey results

A majority (98.1%) of the samples tested were found to be satisfactory. Salmonella spp., E. coli O157, and generic E. coli (>10² CFU/g) were not detected in any of the samples. L. monocytogenes at <5 CFU/g were found in 16 of the 858 (1.9%) samples, however these 16 samples (which were all frozen) represented only 5 unique lot codes of products. The frozen products sampled under this survey had shelf lives of up to 2-years and consequently some lots were sampled multiple times throughout the survey period.

Table 2 – Analysis assessment results
Bacteria	Number of samples tested	Satisfactory	Investigative	Unsatisfactory
L. monocytogenes	858	842	16^{Table Note a}^{Table Note b}	0
Salmonella spp.	858	858	Not applicable	0
E. coli O157	858	858	Not applicable	0
Generic E. coli	858	858	0	Not applicable

Survey results are also presented by country of origin (table 3), and whether the product was frozen or refrigerated at the time of purchase (table 4).

Table 3 – Assessment results by country of origin
Product origin	Number of samples tested (%)	Satisfactory	Investigative
China	347 (40.4)	331	16^{Table Note a}^{Table Note b}
Korea, Republic of	22 (2.6)	22	0
Taiwan	2 (0.2)	2	0
Unknown^{Table Note c} (prepared in Canada)	45 (5.2)	45	0
Unknown^{Table Note c}	442 (51.5)	442	0
Total	858	842	16

Table 4 – Assessment results by product state
Product type	Number of samples tested (%)	Satisfactory	Investigative
Fresh	475 (55.4)	475	0
Frozen	383 (44.6)	367	16^{Table Note a}^{Table Note b}
Total	858	842	16

What the survey results mean

A previous international^Footnote 11 study investigated the presence of a variety of indicator and pathogenic bacteria in brown microalgae. Different from our study, L. monocytogenes was not detected in any of the samples. Differing prevalence rates between studies may be attributable to differences in product types tested, methodology, study design, etc.

Overall, our survey results indicate that seaweed salads sold in Canada are generally safe for consumption. However, as with all food, and especially those that are RTE good hygienic practices are recommended for producers, retailers, and consumers.

What is done with the survey results

All results are used to:

inform risk management decisions
support program design and re-design

While no illnesses were related to the investigative samples, these results triggered appropriate follow-up actions which may have included:

follow-up with the importer
review of manufacturer production, sanitation, and distribution practices
review of records, including product receiving procedures, and previous laboratory test results

Where to access the survey data

The data will be accessible on the Open Government Portal.