Bacterial Pathogens and Indicators in Pasteurized Cheese – April 1, 2018 to March 31, 2021
Food microbiology – Targeted surveys – Final report
A 3-year targeted surveyFootnote 1 analysed 5206 samples of a variety of pasteurized cheese products (soft cheese with spices, single serve cheese, pre-sliced cheese, shredded cheese, firm and hard cheese) for the presence of the pathogens Listeria monocytogenes (L. monocytogenes), Salmonella species (spp.), and Staphylococcus aureus (S. aureus). All samples were also tested for generic Escherichia coli (E. coli) which is an indicator of the hygienic and sanitary conditions of the food supply chain from production to the point of sale.
Over 99.9% of the samples tested were found to be satisfactory. Salmonella spp., was not detected in any of the samples. L. monocytogenes was detected in 1 sample. S. aureus and generic E. coli, both at elevated levels were found in 1 sample each respectively. 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 pasteurized cheese sold in Canada are generally safe for consumption, however they can occasionally be contaminated. Consequently, as with all food, and especially those that are ready for consumption without further preparation or cooking, good hygienic practices are recommended for producers, retailers and consumers.
Why was this survey conducted
The survey was conducted to generate baseline information on the quality and safety of pasteurized cheese sold at retail in Canada. The product types sampled under this survey included softFootnote 2 cheeses with spices, single serve cheeses, pre-sliced cheeses, shredded cheeses, firm,Footnote 2 and hardFootnote 2 cheeses which are all commonly consumed by Canadians of all agesFootnote 3. Unfortunately, many of these foods have been associated with recallsFootnote 4, and foodborne illness outbreaksFootnote 5, Footnote 6, Footnote 7 and are considered to be high-risk foodsFootnote 8.
Contamination with bacterial pathogens can occur at any step in the food supply chain such as during production, processing, packaging, distribution and/or at retail and when consumed, their presence creates the potential for foodborne illness. In an attempt to determine the cumulative effect of each step in the food supply chain on the overall quality and safety of the food, and unique to specific surveys, samples were collected as close to the product best before date as possible.
When was the survey conducted
Where were the samples collected from
Samples were collected from national retail chains and local/regional grocery stores located in the following 11 major cities across Canada:
- Saint John or Moncton
- Quebec City
- Kelowna or Victoria
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.
How many and what kind of samples were collected
A total of 5206 pasteurized cheese samples were collected. A variety of product types were selected to represent a range of moisture content (softFootnote 2, firmFootnote 2 and hardFootnote 2 cheeses) and a varying degree of processing (blocks, sliced, shredded, grated). Of the 5206 samples collected, 1264 were softFootnote 2 cheeses with spices, 1191 were shredded or grated cheeses, 1185 were pre-sliced cheese, 888 were single serve cheeses, and 678 were firmFootnote 2 or hardFootnote 2 cheeses. A sample consisted of a single or multiple consumer sized packages of the same lot weighing at least 250g. Samples were collected as close to the best before date as possible to account for the effects of storage conditions along the food chain.
What were the samples tested for
All samples were tested for L. monocytogenes, Salmonella spp., S. aureus and generic E. coli. L. monocytogenes, Salmonella spp., and S. aureus 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.
What methods were used to tests the samples
Samples were analyzed using analytical methods published in Health Canada's Compendium of Analytical Methods for the Microbiological Analysis of FoodsFootnote 9 that were suitable for the testing of pasteurized cheese.
How were samples assessed
The samples were assessed using criteria based on the principles of following Health Canada documents: Health Products and Food Branch Standards and Guidelines for Microbiological Safety of Foods – An Interpretive SummaryFootnote 10, Policy on Listeria monocytogenes in Ready-to-Eat Foods and the Food and Drugs ActFootnote 11 (Section 4(1)).
|L. monocytogenes||Not detected||Not applicable (category 1 Table Note a)
Detected and ≤ 102 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|
|S. aureus||≤ 102 CFU/g||> 102 and ≤ 104 CFU/g||> 104 CFU/g|
|Generic E. coli||≤ 102 CFU/g||> 102 and ≤ 2x103 CFU/g||> 2x103 CFU/g|
No assessment guidelines had been established in Canada for the presence of Salmonella spp. in pasteurized cheese at the time of writing this report. As this bacteria is considered pathogenic to humans it's presence was assessed as unsatisfactory as it is considered to be a violation of the Food and Drugs ActFootnote 11 Section 4(1)a.
What were the survey results
Over 99.9% of the samples tested were found to be satisfactory. Salmonella spp. was not found in any of the samples tested. L. monocytogenes was detected in 1 sample and at a level of <5 CFU/g. S. aureus at 380 CFU/g and generic E. coli at 300 CFU/g were found in 1 sample each respectively.
|Bacteria||Number of samples tested||Satisfactory (%)||Investigative (%)||Unsatisfactory (%)|
|L. monocytogenes||5206||5203||0||1 Table Note b|
|Salmonella spp.||Not applicable||0|
|S. aureus||1 Table Note c||0|
|Generic E. coli||1 Table Note d||0|
|Total||5206||5203 (99.9)||2 (0.04)||1 (0.02)|
Survey results are also presented by origin (table 3) and product type (table 4).
|Product origin||Number of samples tested (%)||Satisfactory||Investigative||Unsatisfactory|
|Unknown Table Note e||616 (11.8)||615||0||1|
|Unknown Table Note e (domestically processed) Table Note f||416 (8.0)||416||0||0|
|Product type||Number of samples tested (%)||Satisfactory||Investigative||Unsatisfactory|
|Soft cheeseFootnote 2 with spices or other flavour ingredients||1264 (24.3)||1263||0||1 Table Note g|
|Shredded or grated cheese||1191 (22.9)||1191||0||0|
|Pre-sliced cheese||1185 (22.8)||1184||1 Table Note h||0|
|Single serve cheese (blocks, strings, balls)||888 (17.1)||888||0||0|
|FirmFootnote 2 or hardFootnote 2 cheese||678 (13.0)||677||1 Table Note i||0|
What do the survey results mean
Previous CanadianFootnote 12 and internationalFootnote 13 studies on the microbiological quality and safety of retail pasteurized cheeses have shown results approximating those in our study. Differing prevalence rates between studies may be attributable to differences in product types tested, methodology, study design, etc.
Overall, our survey results indicate that pasteurized cheese sold in Canada are generally safe for consumption, however they can be infrequently contaminated. Consequently, as with all foods, and especially with those that are ready for consumption without further preparation or cooking, 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 illness were related to the investigative and unsatisfactory samples, these results triggered appropriate follow-up actions including:
- facility inspections
- additional sampling and testing
- removal of affected products from the marketplace
Can I access the survey data
Yes. The data will be accessible on the Open Government Portal.
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