Table 3.
Overview of the available studies related to the prevalence and concentration of Listeria monocytogenes in blancheda frozen vegetables, with studies in bold type included in the prevalence estimationb
| Reference | Product sampled | Available information on sampling and analytical methodologies | Year of sampling | No of samples tested | No of positive samples | Prevalence (%) | Concentration |
|---|---|---|---|---|---|---|---|
| Literature data | |||||||
| Aguado et al. (2004) | Frozen vegetables (artichoke, green beans, broccoli, carrot, cauliflower, peas, spinach, tomato) | Samples were obtained as final product from a processing plant in ES | 1997–2000 | 906 | 11 | 1.2 | NR |
| Lee et al. (2007b) | Frozen vegetables (Brussels sprouts, onions, peas, peppers, tomatoes) | Samples were taken to reveal the incidence of L. monocytogenes in vegetables processed in Bursa (TR) | NR < 2007 | 44 | 3 | 6.8 | NR |
| Lee et al. (2007a) | Frozen peppers | Samples were taken during four separate visits at monthly intervals over a processing season in a factory (Bursa, TR) that processes and exports frozen strip and cube pepper | NR < 2007 | 12 | 0 | 0.0 | NR |
| Majczyna and Bialasiewicz (2006) | Frozen vegetables | Not provided | 2001–2005 | 62 | 8 | 12.9 | NR |
| Mena et al. (2004) | Frozen vegetables (aubergine, broccoli, courgette, peas, green and red peppers) | Commercial food products were obtained from producers and retailers in PT | 2000–2001 | 271 | 35 | 12.9 | NR |
| Moravkova et al. ( 2017 ) | Frozen vegetables (e.g., peas, carrot, maize; mixed, packed or not packed) | Samples from 32 manufacturers originating from 10 MS were collected in nine supermarkets in CZ | 2014 | 43 | 9 | 20.9 | < 50 CFU/g |
| Moreno et al. ( 2012 ) | Frozen vegetables (spinach, broccoli, stew, stir‐fry) | Samples were collected in supermarkets in Valencia (ES) | NR < 2012 | 33 | 4 | 12.1 | < 100 CFU/g |
| Pappelbaum et al. (2008) | Frozen vegetables (cauliflower, mushrooms, mixed vegetables, broccoli, string bean, green pea, onion, carrot, zucchini, spinach, tomatoes, celery, parsley, paprika, Brussels sprouts) | Samples were collected once a week from a Polish produce processor | 2001–2005 | 1,691 | 791 | 46.8 | NR |
| Skowron et al. (2019) | Frozen vegetable mix (broccoli, carrot, corn, green beans, green pea, pepper, red beans, onion, red and potato) | Samples produced in a freezing plant in PO were yearly tested | 2003–2007 | 9,100 | 504 | 5.5 | NR |
| Vitas et al. (2004) | Frozen vegetables (potatoes, carrot, spinach, broccoli, string‐beans, peas, artichoke, cauliflower) | Samples were obtained in retail outlets of Navarra (ES) | 1997–1999 | 1,750 | 31 | 1.8 | NR |
| Vojkovska et al. ( 2017 ) | Frozen vegetables (broccoli, Brussels sprout, carrot, corn, green beans, green peas, mix, spinach) | Samples were randomly collected from different supermarkets, local stores and green markets in nine cities of CZ | 2014 | 66 | 0 | 0.0 | NR |
| Survey data | |||||||
| Personal communication from Jim McLauchlin from Public Health England (McLauchlin, 2019 ) and poster (Willis et al., 2019 ) | Frozen vegetables (e.g. vegetable mix, peas, sweetcorn, beans, carrot, spinach, peppers, broccoli, sprouts, okra, cauliflower, cabbage, mushrooms, cassava, bitter gourd, onions, squash, asparagus, fenugreek, swede, artichoke, kale, molokhia, yam) |
Sampling focused on catering and retail premises and included any frozen fruit or vegetables Samples (25 g each) were tested for the presence of Listeria species using ISO 11290‐1:2017.6 Identification of Listeria isolates was performed as outlined in the standard methods above |
2019 | 631 | 71 | 11.3 | 2 samples with 20–100 CFU/g, rest < 20 CFU/g |
| Personal communication from Paul Ellis from Public Health Wales (Ellis, 2019 ) | Frozen fruit and vegetables (e.g. sweetcorn, mixed vegetables; broccoli, mushrooms; cauliflower, mixed peppers; carrot, cauliflower, green beans mix, spinach, carrot, peas, sweetcorn mix, butternut squash, melon, peas, cherries and berry smoothie mix) | Enrichment method using 25 g. Direct enumeration was performed in which Listeria species (not monocytogenes) were found in two samples. Sweet corn having 10 CFU/g and chopped onions having 10 CFU/g | 2019 | 265 | 27 | 10.2 | |
| Monitoring data | |||||||
| EU monitoring data (AT, BG, DE, ES, HU) | Pre‐cut frozen vegetables | Monitoring and surveillance at retail level through official sampling using objective sampling (single samples) | 2015–2018 | 118 | 15 | 12.7 | |
| EU monitoring data (BG, CY, FR) | Pre‐cut frozen vegetables | Surveillance and survey at retail level through official sampling using suspect or selective sampling (single or batch samples)c | 2017–2018 | 51 | 11 | 21.6 | |
| EU monitoring data (DE, ES) | Pre‐cut frozen vegetables | Surveillance and survey at packing centre and processing level through official sampling using objective sampling (single samples) | 2015, 2018 | 9 | 3 | 33.3 | |
| EU monitoring data (BG) | Pre‐cut frozen vegetables | Surveillance and monitoring at processing plant through HACCP and own check using objective and census sampling (single and batch samples) | 2015–2017 | 23 | 0 | 0 | |
| Data received through MRA network request | |||||||
| CZ | Frozen vegetables (e.g. spinach, mixed vegetable such as carrot, corn, peas, beans) | Samples were collected from retail; majority were of Czech origin | 2015–2018 | ˜ 100 d | 18 | 18 | < 100 CFU/g |
| CYf | Frozen vegetables (e.g. sweetcorn, mixed vegetables) | Samples were collected from the market (non‐official single samples) | 20 | 6 | 30 | < 10 CFU/g | |
| CYf | Frozen vegetables (e.g. sweetcorn) | Samples were collected from the market (official samples in batches of 5) | 20 | 4 | 20 | < 10 CFU/g | |
| LT | Frozen vegetables (e.g. beans, broccoli, corn, peas, pumpkin cubes, vegetable mix) | Samples were collected at retail (28 samples) and producer (two samples) level in relation to Listeria outbreak from frozen corn in the EU; 24 products were produced in POc | 2018 | 30 | 24 | 80f | < 10 CFU/g or < 40 CFU/ge |
| DEf | Frozen vegetables (broccoli, Brussels sprouts, carrots, cauliflower, mixed vegetables, onions, peas and carrots, spinach, yellow boletus) | Mainly 2018, few 2011 and 2016 | 68 | 12 | 17.6 | ||
MRA: microbiological risk assessment; NR: not reported; RTE: ready‐to‐eat.
Countries: AT: Austria; BG: Bulgaria; CY: Cyprus; CZ: Czechia; DE: Germany; FR: France; HU: Hungary; LT: Lithuania; ES: Spain; PO: Poland; PT: Portugal; TR: Turkey.
Some samples collected in the studies were excluded from the table when these were either not considered vegetables (e.g. parsley in the study by Moreno et al. (2012) or are not blanched according to Appendix A (e.g. leek in the study by Pappelbaum et al. (2008)).
Some studies were excluded to estimate the prevalence because they were only sampled at one processing plant and/or sampling took place before 2010.
These data were excluded to estimate the prevalence because there was evidence that the samples were taken using suspect or selective sampling.
Considered as 100 in the calculation of the prevalence. 17 isolates were of serotype 1/2a and one serotype 1/2b. Data from WGS are available, none of them matched with those of human origin (in 1‐year period).
Each sample consists of five number of units (as ‘n’ in Regulation (EC) 2073/20051). For all the 5 units, L. monocytogenes detection analysis was performed. When Listeria was detected, additionally L. monocytogenes enumeration analysis was done. A sample was considered positive when at least one unit was found positive by detection. In all but two samples, all enumeration results were below the detection limit of 10 CFU/g. In two samples, one unit was < 40 CFU/g.
These data were excluded to estimate the prevalence because they were already retrieved in the monitoring data.