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Listeria monocytogenes in Flavoured Milk - April 1, 2017 to March 31, 2020

Food microbiology - Targeted surveys – Final report

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Summary

Targeted surveys provide information on potential food hazards and enhance the Canadian Food Inspection Agency's (CFIA's) routine monitoring programs. These surveys provide evidence regarding the safety of the food supply, identify potential emerging hazards, and contribute new information and data to food categories where it may be limited or non-existent. They are often used by the agency to focus surveillance on potential areas of higher risk. Surveys can also help to identify trends and provide information about how industry complies with Canadian regulations.

Milk is a nutritious beverage consumed by people of all ages. It is sourced from mammals such as cows, sheep, goats and water buffalo. Flavoured milks (such as chocolate milk) are a popular choice among Canadians as they represent a healthier alternative to soda pops and juices. When compared to unflavoured milk, flavoured milks generally contain additional ingredients such as sugars and flavourings, however they still contain all the nutrients and vitamins found in milk. Consequently, the availability of flavoured milks has increased to meet consumers' demand as Canadians strive to make healthier food choices.

Unfortunately, flavoured milks have been associated with recalls and foodborne illness such as listeriosis outbreaks. In Canada, milk undergoes pasteurization to kill harmful bacteria that may be present in the raw milk. Therefore their presence in the final product may be due a variety of factors such as inadequate pasteurization, or contamination of the milk post-pasteurization. Given that flavoured milks are consumed without further preparation, the possible presence of bacterial pathogens creates the potential for foodborne illness.

Considering the factors mentioned above and their relevance to Canadians, flavoured milks were selected for targeted surveys. The purpose of targeted surveys is to generate baseline information on the occurrence and distribution of pathogenic bacteria in food. Over the course of this study (April 1, 2017 to March 31, 2020), a total of 1495 samples were collected from retail locations in 11 cities across Canada and tested for the bacterial pathogen Listeria monocytogenes (L. monocytogenes). All samples were also tested for Aerobic Colony Count (ACC) which is an indicator of microbial quality. An elevated ACC level (> 5 x 104 Colony Forming Unit (CFU)/g) detected during the shelf life of the product may contribute to spoilage and be an indicator of poor sanitation conditions throughout the food production chain from the rearing conditions of the mammals through to milk production and inadequate control of storage temperatures during transportation to the point of sale or while on display for sale at retail.

L. monocytogenes was not found in any samples, however ACC at elevated (5 x 104 < x ≤ 106 CFU/mL) and high (>106 CFU/mL) levels were found in 17 (1.14%) and 16 (1.07%) samples respectively. The CFIA conducted appropriate follow-up activities. For example, in several cases, follow up inspections were conducted at processing facilities leading to the implementation of corrective actions and in some cases the sampling and testing of additional samples, and in one case a recall was issued. There were no reported illnesses linked to the contaminated products.

Overall, our survey results suggest that the majority of flavoured milks are safe for consumption. Regardless, as this commodity has been linked to foodborne illness and as with all foods, safe handling practices are recommended for producers, retailers and consumers.

What are targeted surveys

Targeted surveys are used by the CFIA to focus its surveillance activities on areas of highest health risk. The information gained from these surveys provides support for the allocation and prioritization of the agency's activities to areas of greater concern. Originally started as a project under the Food Safety Action Plan (FSAP), targeted surveys have been embedded in the CFIA's regular surveillance activities since 2013. Targeted surveys are a valuable tool for generating information on certain hazards in foods, identifying and characterizing new and emerging hazards, informing trend analysis, prompting and refining health risk assessments, highlighting potential contamination issues, as well as assessing and promoting compliance with Canadian regulations.

Food safety is a shared responsibility. The CFIA works with federal, provincial, territorial and municipal governments and provides regulatory oversight of the food industry to promote safe handling of foods throughout the food production chain. The food industry and retail sectors in Canada are responsible for the food they produce and sell, while individual consumers are responsible for the safe handling of the food they have in their possession.

Why did we conduct this survey

Milk is a nutritious beverage consumed by people of all agesFootnote 1. It is sourced from mammals such as cows, sheep, goats and water buffalo. Flavoured milks (such as chocolate milk) are a popular choice among Canadians as they represent a healthier alternative to soda pops and juices. Chocolate milk is also consumed by athletes after intense exercise to aid in recoveryFootnote 2. When compared to unflavoured milk, flavoured milks generally contain additional ingredients such as sugars and flavourings, however they still contain all the nutrients and vitamins found in milk. Consequently, the availability of flavoured milks has increasedFootnote 3 to meet consumers' demand as Canadians strive to make healthier food choices.

Unfortunately, flavoured milks have been associated with recallsFootnote 4 and foodborne illness such as listeriosis outbreaksFootnote 5,Footnote 6,Footnote 7. In Canada milk undergoes pasteurization to kill any harmful bacteria that may be present in the raw milk. Therefore their presence in the final product may be due a variety of factors such as inadequate pasteurization, or contamination of the milk post-pasteurization. Given that flavoured milks are consumed without further preparation, the possible presence of bacterial pathogens creates the potential for foodborne illness.

Considering the factors mentioned above and their relevance to Canadians, flavoured milks were selected for targeted surveys. The purpose of targeted surveys is to generate baseline information on the occurrence and distribution of pathogenic bacteria in food. Over the course of this study (April 1, 2017 to March 31, 2020), a total of 1495 samples were collected from retail locations in 11 cities across Canada and tested for the bacterial pathogen L. monocytogenes. All samples were also tested for ACC which is an indicator of microbial quality. An elevated ACC level (>5 x 104 CFU/g) detected during the shelf life of the product may contribute to spoilage and be an indicator of poor sanitation conditions throughout the food production chain from the rearing conditions of the mammals through to milk production and inadequate storage temperatures during transportation to the point of sale or while on display for sale at retail.

What did we sample

For this survey, a sample consisted of a single unit (individual consumer-size package(s) from a single lot) with a total volume of at least 250 mL. All samples were collected from national retail chains and local/regional grocery stores located in 11 major cities across Canada. These cities encompassed 4 geographical areas: Atlantic (Halifax and Saint John or Moncton), Quebec (Quebec City and Montreal), Ontario (Toronto and Ottawa), and the West (Vancouver, Kelowna or Victoria, Calgary, Saskatoon and Winnipeg). The number of samples collected from these cities was in proportion to the relative population of the respective areas. Samples were collected between April 1, 2017 and March 31, 2020. A variety of flavoured milks were sampled. Samples included conventional and organic product of domestic or imported origin.

What analytical methods were used and how were samples assessed

Samples were analyzed using analytical methods published in Health Canada's Compendium of Analytical Methods for the Microbiological Analysis of FoodsFootnote 8 (table 1). The ACC assessment criteria (table 1) are based on the principles of Health Canada's Health Products and Food Branch Standards and Guidelines for Microbiological Safety of FoodsFootnote 9.

The assessment guidelines for L. monocytogenes are based on Health Canada's Policy on Listeria monocytogenes in RTE foods and is dependent upon the sample type analyzed (Category 1, 2A or 2B)Footnote 10. Fluid milks are considered to be Category 1 products (foods in which the growth of L. monocytogenes can occur).

Table 1 - Analytical methods and assessment criteria for flavoured milk samples
Bacterial analysis Method identification number Table Note a Satisfactory Investigative Unsatisfactory
L. monocytogenes MFLP-28
MFHPB-30
MFLP-77
Absent in 25mL Not applicable (N/A) Detected in 25mL
ACC MFHPB-18 ≤ 5 x 104 CFU/mL 5 x 104 < x ≤ 106 CFU/mL > 106 CFU/mL

Table Notes

Table Note a

The methods used were the published versions at the time of analysis

Return to table note a  referrer

What were the survey results

Over the course of this study (April 1, 2017 to March 31, 2020), a total of 1495 samples were tested for L. monocytogenes and ACC. L. monocytogenes was not found in any samples. ACC at elevated (5 x 104 < x ≤ 106 CFU/mL) and high (> 106 CFU/mL) levels were found in 17/1495 (1.14%) and 16/1495 (1.07%) samples respectively.

Sample assessment results can be found in table 2.

Table 2 - Assessment results of flavoured milk samples
Bacterial analysis Number of samples tested Satisfactory Investigative Unsatisfactory
L. monocytogenes 1495 1462 N/A 0
ACC 17 16
Total (%) 1495 (100) 1462 (97.79) 17 (1.14) 16 (1.07)

A variety of flavours of flavoured milks were analyzed. The flavours most frequently sampled were chocolate (60.4%), strawberry (15.7%) and vanilla (9.0%). Sample assessment results by flavour can be found in table 3.

Table 3 - Assessment results by milk flavour
Milk flavour Number of
samples analyzed
(% total)
Satisfactory Investigative
ACC
5x104 < x ≤ 106 CFU/mL
Unsatisfactory
ACC
> 106 CFU/mL
Chocolate 903 (60.4) 873 17 13
Strawberry 234 (15.7) 233 0 1
Vanilla 135 (9.0) 135 0 0
Banana 74 (4.9) 74 0 0
Caramel, chocolate 45 (3.0) 45 0 0
Coffee 35 (2.3) 35 0 0
Cookies and cream 32 (2.1) 32 0 0
Strawberry, banana 18 (1.2) 17 0 1
Caramel latte 9 (0.6) 9 0 0
Maple 5 (0.3) 5 0 0
Orange cream 2 (0.1) 1 0 1
Chai tea latte 1 (<0.1) 1 0 0
Chocolate, banana 1 (<0.1) 1 0 0
Pumpkin spice 1 (<0.1) 1 0 0
Total 1495 (100) 1462 17 16

Almost all of the samples tested were domestically produced (98.9%), sourced from cows (99.9%) and conventionally produced (98.9%). Sample assessment results by country of origin, animal source and production practice can be found in tables 4, 5 and 6 respectively.

Table 4 - Assessment results by country of origin
Country of origin Satisfactory Investigative
ACC
5x104 < x ≤ 106 CFU/mL
Unsatisfactory
ACC
> 106 CFU/mL
Total (%)
Canada 1445 17 16 1478 (98.86)
United States 17 0 0 17 (1.14)
Total 1462 17 16 1495 (100)
Table 5 - Assessment results by animal source
Animal source Satisfactory Investigative
ACC
5x104 < x ≤ 106 CFU/mL
Unsatisfactory
ACC
> 106 CFU/mL
Total (%)
Cow 1461 16 16 1493 (99.9)
Sheep 1 0 0 1 (<0.1)
Water buffalo 0 1 0 1 (<0.1)
Total 1462 17 17 1495 (100)
Table 6 - Assessment results by production practice
Production practice Satisfactory Investigative
ACC
5x104 < x ≤ 106 CFU/mL
Unsatisfactory
ACC
> 106 CFU/mL
Total (%)
Conventional 1380 10 14 1404 (93.9)
Organic 82 7 2 91 (6.1)
Total 1462 17 16 1495 (100)

Details about each investigative sample are provided in table 7.

Table 7 - Detailed information about investigative samples
Milk flavour ACC level (CFU/mL) Number of days tested prior to best before date Milk fat (%) Country of origin Source animal Production practice
Chocolate 8.6 x 105 3 3.5 Canada Cow Organic
Chocolate 3.3 x 105 6 1 Canada Cow Conventional
Chocolate 9.6 x 105 8 3.8 Canada Cow Organic
Chocolate 2.1 x 105 12 8 Canada Water buffalo Conventional
Chocolate ~1.3 x 105 7 2 Canada Cow Organic
Chocolate ~5.5 x 104 4 3.25 Canada Cow Conventional
Chocolate 8.4 x 105 3 3.8 Canada Cow Organic
Chocolate Table Note b 2.1 x 105 1 1 Canada Cow Conventional
Chocolate 3.0 x 105 4 1 Canada Cow Conventional
Chocolate ~1.1 x 105 0 3.25 Canada Cow Conventional
Chocolate 4.2 x 105 6 3.25 Canada Cow Conventional
Chocolate 6.8 x 105 -2 Table Note c 2 Canada Cow Conventional
Chocolate ~7.5 x 104 1 2 Canada Cow Conventional
Chocolate ~8.0 x 104 7 3.8 Canada Cow Organic
Chocolate ~5.5 x 104 7 3.8 Canada Cow Organic
Chocolate 2.2 x 105 5 1 Canada Cow Conventional
Chocolate 2.9 x 105 7 3.8 Canada Cow Organic

Table Notes

Table Note b

Ultra-high-temperature (UHT) pasteurized

Return to table note b  referrer

Table Note c

sample tested 2 days after the best before date

Return to table note c  referrer

Details about each unsatisfactory sample are provided in table 8.

Table 8 - Detailed information about unsatisfactory samples
Ice cream flavour ACC level (CFU/mL) Number of days tested prior to best before date Milk fat (%) Country of origin Source animal Production practice
Chocolate 2.3 x 107 0 1 Canada Cow Conventional
Orange Cream Table Note d ~4.1 x 108 20 1 Canada Cow Conventional
Chocolate 6.0 x 106 7 1 Canada Cow Conventional
Chocolate 1.9 x 106 10 1 Canada Cow Conventional
Strawberry 3.9 x 107 2 1 Canada Cow Conventional
Chocolate ~3.2 x 108 27 3.6 Canada Cow Conventional
Chocolate 4.3 x 107 5 3.5 Canada Cow Organic
Chocolate 1.6 x 106 3 2 Canada Cow Conventional
Chocolate 4.2 x 106 5 3.6 Canada Cow Conventional
Chocolate 1.5 x 106 9 2 Canada Cow Conventional
Chocolate 1.9 x 106 9 2 Canada Cow Conventional
Strawberry Table Note d 5.4 x 106 78 Skim (0-0.5) Canada Cow Conventional
Chocolate 3.7 x 106 5 3.5 Canada Cow Organic
Chocolate 3.7 x 106 6 2 Canada Cow Conventional
Chocolate 2.6 x 106 4 1 Canada Cow Conventional
Chocolate 2.7 x 107 4 2 Canada Cow Conventional

Table Notes

Table note d

UHT pasteurized

Return to table note d  referrer

What do the survey results mean

In this survey, 97.79% of the flavoured milk samples analyzed were assessed as satisfactory. L. monocytogenes was not found in any samples. ACC at elevated (5 x 104 < x ≤ 106 CFU/mL) and high (> 106 CFU/mL) levels were found in 17 (1.14%) and 16 (1.07%) samples respectively.

L. monocytogenes was not found in any of the flavoured milk samples (0/1495) in our survey. Similar results were found in a US studyFootnote 11 conducted in 2000 that investigated the presence of L. monocytogenes in 1669 pasteurized chocolate milk samples collected from a variety of retail stores near their sell-by date. L. monocytogenes was not detected in any of these US produced chocolate milk samples (0/1669).

The levels of ACC found in the samples tested in our survey are similar to those previously reported in a US studyFootnote 12 conducted during 1996 and 1997 which tested the standard plate counts (SPC) of both unflavoured and chocolate milk samples from four production plants at various time points throughout their shelf life. On the day of production, the SPC counts of all samples (unflavoured and chocolate) were not significantly different (P > 0.001) with SPCs <1000 CFU/mL. By day 14 post production, the SPC of chocolate milk samples were significantly higher (P < 0.001) than the SPC of unflavoured milk samples with 53.7% and 26.1% of the samples >106 CFU/g, respectively.

The CFIA conducted appropriate follow-up activities. In several cases, follow up inspections were conducted at processing facilities leading to the implementation of corrective actions and in some cases additional samples were tested, and in one case a recall was issued. There were no reported illnesses linked to the contaminated products.

Overall, our survey results suggest that the majority of flavoured milks are safe for consumption. Regardless, as this commodity has been linked to foodborne illness and as with all foods, safe handling practices are recommended for producers, retailers and consumers.

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