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Bacterial Pathogens in Dried Herbs and Dried Teas - April 1, 2014 to March 31, 2018

Food microbiology - Targeted Surveys - Final report

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Summary

Dried aromatic herbs are widely used flavoring ingredients in food preparations. Dried teas including teas and herbal teas are used for brewing teas. Both dried herbs and teas are consumed globally and traded internationally. Dried herbs have been associated with numerous salmonellosis outbreaks worldwide, and dried teas have recently been associated with several recalls due to Salmonella contamination and a salmonellosis outbreak. Both dried herbs and teas are derived from agricultural products and can be contaminated with bacterial pathogens during primary production, processing, storage and packaging. Once contaminated, bacterial pathogens, such as Salmonella can survive for extended periods of time in these low-moisture products. Depending on the end use, for example if dried herbs are added to ready-to-eat (RTE) foods that undergo no further heat treatment, or dried teas are cold-brewed, the presence of bacterial pathogens creates a potential risk for foodborne illnesses.

Considering the factors mentioned above and their relevance to Canadians, dried herbs and dried teas were selected for targeted surveys. The purpose of this survey was to generate baseline information on the occurrence of pathogenic bacteria of concern in dried herb and tea products on the Canadian market.

Over the course of this study (April 1, 2014 to March 31, 2018), a total of 2680 dried herb samples and 1178 dried tea samples were collected from retail locations in 11 cities across Canada. All herb (2680) and tea (1178) samples were tested for generic Escherichia coli (E. coli) and the following bacterial pathogens: Salmonella species (spp.), Bacillus cereus (B. cereus) and Clostridium perfringens (C. perfringens). A portion of the dried herb samples (1773) and all of the dried tea samples (1178) were also tested for the bacterial pathogen Staphylococcus aureus (S. aureus). Generic E. coli is an indicator of the overall sanitation conditions throughout the food chain from production to the point of sale.

In this study, over 99.8% of the dried herb samples and over 99.5% of the dried tea samples were assessed as satisfactory. Presumptive B. cereus was found at elevated levels (104 < x ≤ 106 colony-forming units (CFU)/gram (g)) in two herb samples (0.07%, 2/2680) and five tea samples (0.4%, 5/1178). S. aureus was found at elevated levels (102 < x ≤ 104 CFU/g) in one herb sample (0.06% 1/1773). Salmonella spp. was identified in one herb sample (0.04%, 1/2680) and one tea sample (0.08%, 1/1178). High levels (> 103 most probable number (MPN)/g) of generic E. coli were found in two herb samples (0.07%, 2/2680).

In dried herb and tea products, the presence of elevated levels B. cereus (104 < x ≤ 106 CFU/g) or S. aureus (102 < x ≤ 104 CFU/g) could indicate that the food may have been produced under unsanitary conditions. The presence of high levels (>103 MPN/g) of generic E. coli could indicate inadequate sanitation controls during processing and/or at the processing facility.

The Canadian Food Inspection Agency (CFIA) conducted appropriate follow-up activities such as facility inspections and additional sampling. The Salmonella contaminated herb and tea samples resulted in product recalls. The two herb samples where high levels of generic E. coli were found resulted in the implementation of corrective actions by the processing facilities and one product recall as the product was considered to be RTE. There were no known reported illnesses associated with any of the contaminated herb or tea products.

Overall, our survey results indicate that most of the dried herbs and dried teas sampled appear to have been produced under sanitary conditions. However, contamination by bacterial pathogens such as Salmonella can occur occasionally, and a loss of sanitation controls along the food production chain can occur as well. Consequently, 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?

Dried herbs are widely used flavoring ingredients in food preparations. Dried teas including teas (green, white, black and oolong) and herbal teas (blended herbs, spices and other plant material) are used for brewing teas. Dried herbs have been associated with numerous foodborne illness outbreaks worldwideFootnote 1 Footnote 2, and dried teas have recentlyFootnote 3 Footnote 4 been associated with several recalls due to Salmonella contamination and a salmonellosis outbreak Footnote 5. Both dried herbs and teas are derived from agricultural products and can be contaminated with bacterial pathogens during primary production, processing, storage and packaging. In addition, dried herbs and teas are consumed all over the world and are traded internationallyFootnote 6. Contaminated products can be distributed internationally and potentially cause foodborne illnesses in multiple countries. Depending on the end use of the product, for example, if dried herbs are added to RTE foods that undergo no further heat treatment, or dried teas are cold-brewed, the presence of bacterial pathogens creates a potential risk for foodborne illnesses.

Considering the factors mentioned above and their relevance to Canadians, dried herbs and dried teas were selected for targeted surveys. The purpose of this survey was to generate baseline information on the occurrence of generic E. coli and the following pathogenic bacteria: Salmonella spp., B. cereus, C. perfringens and S. aureus in dried herb and tea products on the Canadian market. Generic E. coli is an indicator of the overall sanitation conditions throughout the food chain from production to the point of sale.

What did we sample?

A sample consisted of a single or multiple unit(s) (individual consumer-size package(s) from a single lot) with a total weight of at least 100 g. All samples were collected from national and local/regional retail stores located in 11 major cities across Canada. These cities encompassed four geographical areas:

  • Atlantic (Halifax and Saint John)
  • Quebec (Quebec City, Montreal)
  • Ontario (Toronto, Ottawa)
  • West (Vancouver, Kelowna, Calgary, Saskatoon and Winnipeg).

The number of samples collected from these cities was in proportion to the relative population of the respective areas.

Dried herb samples were collected between April 1, 2014 to March 31, 2015 and April 1, 2016 to March 31, 2018. Dried tea samples including dried teas and dried herbal teas (blended herbs, spices or other plant material) were collected between April 1, 2016 and March 31, 2018. Sample collection and testing information can be found in table 1.

Table 1- Sample collection and testing of dried herbs and dried teas
Product group Survey year(s) Analyses Number of samples analyzed
Dried herbs
(group i)
2014-2015 B. cereus
C. perfringens
Salmonella spp.
Generic E. coli
907
Dried herbs
(group ii)
2016-2017
2017-2018
B. cereus
C. perfringens
S. aureus
Salmonella spp.
Generic E. coli
1773
Subtotal (dried herbs) 2680
Dried teas 2016-2017
2017-2018
B. cereus
C. perfringens
S. aureus
Salmonella spp.
Generic E. coli
1178
Total 3858

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 7. The assessment criteria used in this survey are based on the principles of the Health Products and Food Branch Standards and Guidelines for Microbiological Safety of Foods Footnote 8. At the time of writing this report, no assessment guidelines had been established in Canada for the presence of pathogenic bacteria in dried herbs and dried teas. Health Canada's guidelines for indicator organisms and bacterial pathogens in spices (ready-to-eat) Footnote 8 were applied in the assessment of dried herb and tea results (table 2).

Table 2 - Analytical methods and assessment criteria for bacteria in dried herbs and dried teas
Bacterial analysis Method identification number Table Note a Satisfactory assessment Investigative assessment Unsatisfactory assessment
Bacillus cereus MFLP-42 ≤ 104 CFU/g 104 < x ≤ 106 CFU/g > 106 CFU/g
Clostridium perfringens MFHHPB-23 ≤ 104 CFU/g 104 < x ≤ 106 CFU/g > 106 CFU/g
Staphylococcus aureus MFHPB-21 ≤ 102 CFU/g 102 < x ≤ 104 CFU/g > 104 CFU/g
Salmonella spp. MFHPB-20 Absent in 25 g Not Applicable (N/A) Present in 25 g
Generic E. coli MFHPB-19 ≤ 102 MPN/g 102 < x ≤ 103 MPN/g > 103 MPN/g

Table Notes

Table note a

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

Return to table note a  referrer

B. cereus, C. perfringens and S. aureus are commonly found in the environment and are bacteria that can produce protein toxins in contaminated food or in the intestines of infected humans, which can cause foodborne illness. Elevated levels of these bacteria (table 2) indicate that the food may have been produced under unsanitary conditions. Therefore,an investigative assessment which may result in further follow-up actions is associated with elevated levels of the bacteria. As the results are based on the analysis of one unit (n=1), further sampling may be required to verify the levels of the bacteria of the lot. The presence of high levels of these bacteria (table 2) is indicative of high enough levels of the bacterial toxins to cause foodborne illnesses. Therefore, samples with high levels of the bacteria are assessed as unsatisfactory indicating that follow-up activities are warranted. The B. cereus method used in this survey is unable to discriminate B. cereus from other closely related organisms and therefore results are considered presumptive for B. cereus.

Unlike harmful bacterial pathogens such as Salmonella spp., generic E. coli is commonly found in the intestines of humans and most strains are harmless. It is considered to be an indicator organism and levels of generic E. coli found in a food product are used to assess the overall sanitation conditions throughout the food chain from production to the point of sale. An investigative assessment is associated with elevated levels of generic E. coli (100 < x ≤ 1000 most probable number (MPN)/g), which may result in further follow-up actions. As the results are based on the analysis of one unit (n=1), further sampling may be required to verify the levels of generic E. coli of the lot. An unsatisfactory assessment is associated with high levels of generic E. coli (> 1000 MPN/g) as it may indicate a breakdown in good manufacturing practices (sanitation practices), and therefore possibly warranting the initiation of follow-up activities.

What were the survey results?

Group i dried herb samples (907) were tested for generic E. coli and the bacterial pathogens B. cereus, C. perfringens and Salmonella spp. (table 3). Group ii dried herb samples (1773) were tested for generic E. coli and the bacterial pathogens B. cereus, C. perfringens, S. aureus and Salmonella spp. C. perfringens (>104 CFU/g) was not found in any of the herb samples (2680). Presumptive B. cereus was found at elevated levels (104 < x ≤ 106 CFU/g) in two herb samples(0.07%, 2/2680). S. aureus was found at elevated levels (102 < x ≤ 104 CFU/g) in one herb sample (0.06% 1/1773). Salmonella spp. was identified in one herb sample (0.04%, 1/2680), which also contained an elevated level (102 < x ≤ 103 MPN/g) of generic E. coli. High levels (>103 MPN/g) of generic E. coli were found in two herb samples (0.07%, 2/2680).

All of the dried tea samples (1178) were tested for generic E. coli and the bacterial pathogens B. cereus, C. perfringens, S. aureus and Salmonella spp. (table 3). C. perfringens (>104 CFU/g), S. aureus (>102 CFU/g) and generic E. coli (>102 MPN/g) were not found in any of the tea samples. Presumptive B. cereus were found at elevated levels (104 < x ≤ 106 CFU/g) in five tea samples(0.4%, 5/1178). Salmonella spp. was identified in one tea sample (0.08%, 1/1178).

Table 3 - Results of bacterial analysis in dried herb and dried tea samples
Analysis group Analysis Unsatisfactory
(% of total samples)
Investigative
(% of total samples)
Satisfactory (% of total samples) Number of samples tested
Dried herbs (group i) B. cereus 0 2 903 907
C. perfringens 0 0
Salmonella spp. 1 Table Note b N/A
Generic E. coli 1 0
Dried herbs (group ii) B. cereus 0 0 1771 1773
C. perfringens 0 0
S. aureus 0 1
Salmonella spp. 0 N/A
Generic E. coli 1 0
Subtotal (dried herbs) 3 (0.1%) 3 (0.1%) 2674 (99.8%) 2680 (100%)
Dried teas B. cereus 0 5 1172 1178
C. perfringens 0 0
S. aureus 0 0
Salmonella spp. 1 N/A
Generic E. coli 0 0
Subtotal (dried teas) 1 (0.1%) 5 (0.4%) 1172 (99.5%) 1178 (100%)
Total 4 (0.1%) 8 (0.2%) 3846 (99.7%) 3858 (100%)

Table Notes

Table note b

Elevated level (102-103 MPN/g) of generic E. coli also present.

Return to table note b  referrer

Of the 2680 dried herb samples 6.7% were domestic and 67.7% were imported from more than 25 countries. The country where the product was processed could not be determined for 25.7% of the samples (table 4). Of the 1178 dried tea samples 19.0% were domestic and 59.2% were imported from more than 15 countries. The country where the product was processed could not be determined for 21.8% of the samples (table 5). In terms of production practice, 64.1% of dried herb samples and 68.2% of dried tea samples were conventional (tables 4 and 5).

Table 4 - Product origin and production practice of dried herb samples
Product origin Total number of samples (%) Conventional Organic
Domestic 179 (6.7) 158 21
Imported 1812 (67.6) 921 891
Argentina 5 0 5
Croatia 2 0 2
Egypt 147 5 142
France 3 0 3
Germany 2 2 0
Greece 13 12 1
India 37 28 9
Iran 4 4 0
Israel 13 2 11
Italy 7 0 7
Lebanon 9 9 0
Morocco 28 14 14
Netherland 2 0 2
Norway 6 0 6
Peru 4 0 4
Poland 12 9 3
Romania 5 0 5
Sri Lanka 2 0 2
Tunisia 3 0 3
Turkey 64 26 38
United States 120 6 114
Other Table Note c 5 2 3
Imported unknown 1319 801 518
Unknown 689 (25.7) 639 (1 Table Note d) 50
Total 2680 (100) 1718 (64.1) 962 (35.9)

Table Notes

Table note c

Number of countries which represented only one sample

Return to table note c  referrer

Table note d

Salmonella contaminated sample

Return to table note d  referrer

Table 5 - Product origin and production practice of dried tea samples
Product origin Total number of samples (%) Conventional Organic
Domestic 224 (19.0) 192 (1 Table Note f) 32
Imported 697 (59.2) 468 229
Argentina 4 2 2
China 57 31 26
Egypt 22 7 15
France 10 5 5
Germany 80 61 19
Greece 2 1 1
India 76 25 51
Japan 6 6 0
Kenya 55 55 0
Lebanon 15 15 0
European Union 10 10 0
South Africa 5 1 4
Poland 18 18 0
Sri Lanka 133 131 2
Vietnam 2 0 2
United Kingdom 20 20 0
United States 80 21 59
Multiple 2 1 1
Other Table Note e 6 5 2
Imported unknown 94 53 41
Unknown 257 (21.8) 143 114
Total 1178 (100) 803 (68.2) 375 (31.8)

Table Notes

Table note e

Number of countries which represented only one sample

Return to table note e  referrer

Table note f

Salmonella contaminated sample

Return to table note f  referrer

Dried herb and dried tea product types are detailed in table 6. A variety of dried herbs were collected representing 14 single and three mixed types (table 6). Dried tea samples were categorized into five tea types (black, green, oolong, white, and herbal) (table 7). Herbal teas (blended herbs, spices and other plant material) accounted for 51.4% of the dried tea samples.

Table 6 - Product types of dried herb samples
Product type Number of samples % of total
Basil 375 14
Bay leaves 1 0.03
Chive 1 0.03
Cilantro 236 8.8
Dill 110 4.1
Marjoram 37 1.4
Mint 12 0.4
Oregano 436 16.3
Parsley 157 5.9
Rosemary 381 14.2
Sage 231 8.6
Savoury 72 2.7
Tarragon 37 1.4
Thyme 478 17.8
Herbs of provence 10 0.4
Mixed italian herbs 31 1.3
Mixed herbs 75 2.8
Total 2680 100
Table 7 - Product types of dried tea samples
Product type Tea types Number of samples % of total
Teas Black tea 298 25.3
Teas Green tea 227 19.3
Teas Oolong tea 21 1.8
Teas White tea 27 2.3
Herbal tea n/a 605 51.4
Total 1178 100

Further details of each unsatisfactory and investigative sample are provided in table 8.

Table 8 - Product types of unsatisfactory and investigative samples
Product type Unsatisfactory
Salmonella
Unsatisfactory
Generic E. coli
>103 CFU/g
Investigative
B. cereus
104 < x ≤ 106 CFU/g
Investigative
S. aureus
102 < x ≤ 104 CFU/g
Number of samples tested per product type
Dried oregano (RTE) 0 1 1 0 436
Dried rosemary 1 1 0 0 381
Dried savory 0 0 1 0 72
Dried tarragon 0 0 0 1 37
Dried herbal tea 1 Table Note g 0 2 0 605
Dried green tea 0 0 1 0 227
Dried black tea 0 0 1 0 297
Dried white tea 0 0 1 0 27
Total 2 2 7 1 N/A

Table Notes

Table note g

Elevated level (102 < x ≤103 CFU/g) of generic E. coli also present

Return to table note g  referrer

What do the survey results mean?

In this study, over 99.8% of the dried herb samples and over 99.5% of the dried tea samples were assessed as satisfactory. C. perfringens (>104 CFU/g) was not found in any of the herb samples (2680). C. perfringens (>104 CFU/g), S. aureus (>102 CFU/g),and generic E. coli (>102 CFU/g) were not found in any of the tea samples (1178).

Salmonella spp., a common bacterial pathogen associated with foodborne illnesses, was identified in 0.04% (1/2680) of the herb samples and 0.08% (1/1178) of the tea samples. All Salmonella contaminated samples resulted in product recalls. B. cereus, a common bacterial pathogen in low-moisture foods, was found at elevated levels (104 < x ≤ 106 CFU/g) in 0.07% (2/2680) of the herb samplesand 0.4% (5/1178) of the tea samples. S. aureus was found at an elevated level (102 < x ≤ 104 CFU/g) in 0.06% (1/1173) of the herb samples. Samples where elevated levels of S. aureus and presumptive B. cereus were found could indicate that the food may have been produced under unsanitary conditions. High levels of generic E. coli (> 103 CFU/g) were found in 0.07% (2/2680) of the herb samples resulting in the implementation of corrective actions by the processing facilities and one product recall. There were no known reported illnesses associated with the any of the contaminated dried herb and dried tea products.

The prevalence of Salmonella spp. (0.04%, 95% CI: 0.01-0.21%) in dried herb samples identified in this survey appears slightly lower than the prevalence reported in a study conducted in the US. The US studyFootnote 9 investigated the prevalence of Salmonella in dried herbs collected from retail locations in the US between 2013 and 2014 and found Salmonella in 0.23% (4/1741, 95% CI: 0.09-0.59%) of the dried herb samples (basil, coriander, and oregano). A similar study conducted in the UK in 2004 reported the prevalence of Salmonella as being 1.21% (9/743, 95% CI: 0.64-2.29%) in retail dried herb samples (coriander, fenugreek, mint and sage). The UK study also reported the prevalence of B. cereus (and other Bacillus spp.)at levels >104 CFU/g as being 0.27% (2/743, 95% CI: 0.07-0.98%) in retail dried herbs. In comparison, the prevalence of presumptive B. cereus at levels >104 CFU/g (and below ≤ 106 CFU/g) was found to be 0.07% (2/2680, 95% CI: 0.02-0.27%) in retail dried herb samples (14 single and three mixed types) analysed in this study.

The prevalence of Salmonella spp. (0.08%, 95% CI: 0.01-0.48%) and presumptive B. cereus (0.4%, 95% CI: 0.18-0.99%) at elevated levels (104 < x ≤ 106 CFU/g) in dried tea samples were identified in the current study. To date, very few published studies investigating the microbiological safety and quality of dried teas have been conducted as dried teas have traditionally been brewed using boiling or hot water, serving as an effective microbial risk mitigation step. More recently, brewing teas in low temperature or ice water has become a common practice. A study Footnote 10 revealed that using boiling water or hot water (>80 °C) to brew teas from one to several minutes resulted in the complete inactivation of bacterial pathogens such as Salmonella from brewed teas Footnote 10. The study did discover that the use of low temperature water (below 55°C) to brew teas did not inactivate all of the bacterial pathogens Footnote 10. The study results Footnote 10 suggest that the practice of using low temperature water to brew teas contaminated with pathogens may result in foodborne illnesses in high risk population (such as infants Footnote 5 , elderly and people with a weak immune system).

Overall, our survey results indicate that most dried herb and dried tea products sampled appear to have been produced under sanitary conditions. However, our results do indicate that contamination by bacterial pathogens such as Salmonella can occur occasionally, and a loss of sanitation controls along the food production chain can occur as well. Consequently, as with all foods, safe handling practices are recommended for producers, retailers and consumers.

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