1887
Research Open Access
Like 0

Abstract

Background

Most infections in humans are considered foodborne, but the relative importance of the various routes of infection is largely unknown. Consumption of green produce contaminated with oocysts has been identified as a possible source.

Aim

We aimed to estimate the occurrence and prevalence of oocysts in commercially available ready-to-eat (RTE) salad mixes in 10 European countries.

Methods

A real-time PCR-based method for oocyst detection was developed and optimised by two laboratories and validated in an interlaboratory test. This detection method and a harmonised sampling strategy were applied in a multi-country study. Multivariable logistic regression was used to investigate risk factors for oocyst contamination of RTE salad.

Results

The real-time PCR method had a detection limit of 10 oocysts per 30 g of salad. We collected 3,329 RTE salad samples (baby leaf and cut leaf mixes) from October 2021 to September 2022. The prevalence of oocyst contamination was 4.1% (95% confidence interval (CI): 3.4–4.8%; n = 3,293). In multivariable regression analysis, winter season, sampling and packaging of salad in Northern Europe and production of salad in Western Europe were associated with detection of , with no statistically significant differences between salad types.

Conclusion

We estimated the prevalence of oocysts in RTE leafy green salads using a validated and standardised procedure to assess the potential risk for human infection; highlighting the need to address this risk at each critical point of the salad production chain.

Loading

Article metrics loading...

/content/10.2807/1560-7917.ES.2025.30.22.2400594
2025-06-05
2025-06-07
/content/10.2807/1560-7917.ES.2025.30.22.2400594
Loading
Loading full text...

Full text loading...

/deliver/fulltext/eurosurveillance/30/22/eurosurv-30-22-3.html?itemId=/content/10.2807/1560-7917.ES.2025.30.22.2400594&mimeType=html&fmt=ahah

References

  1. Dubey JP. Toxoplasmosis of Animals and Humans. 3rd ed. Boca Ratón: CRC Press; 2021.
  2. Hald T, Aspinall W, Devleesschauwer B, Cooke R, Corrigan T, Havelaar AH, et al. World Health Organization estimates of the relative contributions of food to the burden of disease due to selected foodborne hazards: a structured expert elicitation. PLoS One. 2016;11(1):e0145839.  https://doi.org/10.1371/journal.pone.0145839  PMID: 26784029 
  3. Pinto-Ferreira F, Caldart ET, Pasquali AKS, Mitsuka-Breganó R, Freire RL, Navarro IT. Patterns of transmission and sources of infection in outbreaks of human toxoplasmosis. Emerg Infect Dis. 2019;25(12):2177-82.  https://doi.org/10.3201/eid2512.181565  PMID: 31742524 
  4. Garweg JG, Kieffer F, Mandelbrot L, Peyron F, Wallon M. Long-term outcomes in children with congenital toxoplasmosis-a systematic review. Pathogens. 2022;11(10):1187.  https://doi.org/10.3390/pathogens11101187  PMID: 36297244 
  5. EFSA Panel on Biological Hazards (BIOHAZ)Koutsoumanis K, Allende A, Alvarez-Ordóñez A, Bolton D, Bover-Cid S, et al. Public health risks associated with food-borne parasites. EFSA J. 2018;16(12):e05495. PMID: 32625781 
  6. Flegr J, Prandota J, Sovičková M, Israili ZH. Toxoplasmosis--a global threat. Correlation of latent toxoplasmosis with specific disease burden in a set of 88 countries. PLoS One. 2014;9(3):e90203.  https://doi.org/10.1371/journal.pone.0090203  PMID: 24662942 
  7. European Food Safety Authority (EFSA)European Centre for Disease Prevention and Control (ECDC). The European Union One Health 2023 Zoonoses report. EFSA J. 2024;22(12):e9106. PMID: 39659847 
  8. Cassini A, Colzani E, Pini A, Mangen MJ, Plass D, McDonald SA, et al. Impact of infectious diseases on population health using incidence-based disability-adjusted life years (DALYs): results from the Burden of Communicable Diseases in Europe study, European Union and European Economic Area countries, 2009 to 2013. Euro Surveill. 2018;23(16):17-00454.  https://doi.org/10.2807/1560-7917.ES.2018.23.16.17-00454  PMID: 29692315 
  9. López Ureña NM, Chaudhry U, Calero Bernal R, Cano Alsua S, Messina D, Evangelista F, et al. Contamination of soil, water, fresh produce, and bivalve mollusks with Toxoplasma gondii oocysts: a systematic review. Microorganisms. 2022;10(3):517.  https://doi.org/10.3390/microorganisms10030517  PMID: 35336093 
  10. Dámek F, Swart A, Waap H, Jokelainen P, Le Roux D, Deksne G, et al. Systematic review and modelling of age-dependent prevalence of Toxoplasma gondii in livestock, wildlife and felids in Europe. Pathogens. 2023;12(1):97.  https://doi.org/10.3390/pathogens12010097  PMID: 36678447 
  11. Caradonna T, Marangi M, Del Chierico F, Ferrari N, Reddel S, Bracaglia G, et al. Detection and prevalence of protozoan parasites in ready-to-eat packaged salads on sale in Italy. Food Microbiol. 2017;67:67-75.  https://doi.org/10.1016/j.fm.2017.06.006  PMID: 28648295 
  12. Betts R. Microbial update: fruit and salad. Int Food Hyg. 2014;25(3):9-12.
  13. Slana I, Bier N, Bartosova B, Marucci G, Possenti A, Mayer-Scholl A, et al. Molecular methods for the detection of Toxoplasma gondii oocysts in fresh produce: an extensive review. Microorganisms. 2021;9(1):167.  https://doi.org/10.3390/microorganisms9010167  PMID: 33451081 
  14. Wainwright KE, Miller MA, Barr BC, Gardner IA, Melli AC, Essert T, et al. Chemical inactivation of Toxoplasma gondii oocysts in water. J Parasitol. 2007;93(4):925-31.  https://doi.org/10.1645/GE-1063R.1  PMID: 17918377 
  15. Dubey JP, Swan GV, Frenkel JK. A simplified method for isolation of Toxoplasma gondii from the feces of cats. J Parasitol. 1972;58(5):1005-6.  https://doi.org/10.2307/3286603  PMID: 5078580 
  16. Lalle M, Possenti A, Dubey JP, Pozio E. Loop-Mediated Isothermal Amplification-Lateral-Flow Dipstick (LAMP-LFD) to detect Toxoplasma gondii oocyst in ready-to-eat salad. Food Microbiol. 2018;70:137-42.  https://doi.org/10.1016/j.fm.2017.10.001  PMID: 29173620 
  17. Slany M, Dziedzinska R, Babak V, Kralik P, Moravkova M, Slana I. Toxoplasma gondii in vegetables from fields and farm storage facilities in the Czech Republic. FEMS Microbiol Lett. 2019;366(14):fnz170.  https://doi.org/10.1093/femsle/fnz170  PMID: 31365074 
  18. Cazeaux C, Lalle M, Durand L, Aubert D, Favennec L, Dubey JP, et al. Evaluation of real-time qPCR-based methods to detect the DNA of the three protozoan parasites Cryptosporidium parvum, Giardia duodenalis and Toxoplasma gondii in the tissue and hemolymph of blue mussels (M. edulis). Food Microbiol. 2022;102:103870.  https://doi.org/10.1016/j.fm.2021.103870  PMID: 34809958 
  19. United Nations Statistics Division (UNSD). Standard country or area codes for statistical use (M49). New York: UNSD. [Accessed: 3 Jun 2025]. Available from: https://unstats.un.org/unsd/methodology/m49
  20. Hurtado A, Aduriz G, Moreno B, Barandika J, García-Pérez AL. Single tube nested PCR for the detection of Toxoplasma gondii in fetal tissues from naturally aborted ewes. Vet Parasitol. 2001;102(1-2):17-27.  https://doi.org/10.1016/S0304-4017(01)00526-X  PMID: 11705648 
  21. Joeres M, Cardron G, Passebosc-Faure K, Plault N, Fernández-Escobar M, Hamilton CM, et al. A ring trial to harmonize Toxoplasma gondii microsatellite typing: comparative analysis of results and recommendations for optimization. Eur J Clin Microbiol Infect Dis. 2023;42(7):803-18.  https://doi.org/10.1007/s10096-023-04597-7  PMID: 37093325 
  22. Burg JL, Grover CM, Pouletty P, Boothroyd JC. Direct and sensitive detection of a pathogenic protozoan, Toxoplasma gondii, by polymerase chain reaction. J Clin Microbiol. 1989;27(8):1787-92.  https://doi.org/10.1128/jcm.27.8.1787-1792.1989  PMID: 2768467 
  23. Homan WL, Vercammen M, De Braekeleer J, Verschueren H. Identification of a 200- to 300-fold repetitive 529 bp DNA fragment in Toxoplasma gondii, and its use for diagnostic and quantitative PCR. Int J Parasitol. 2000;30(1):69-75.  https://doi.org/10.1016/S0020-7519(99)00170-8  PMID: 10675747 
  24. Shapiro K, Bahia-Oliveira L, Dixon B, Dumètre A, de Wit LA, VanWormer E, et al. Environmental transmission of Toxoplasma gondii: Oocysts in water, soil and food. Food Waterborne Parasitol. 2019;15:e00049.  https://doi.org/10.1016/j.fawpar.2019.e00049  PMID: 32095620 
  25. Lalonde LF, Gajadhar AA. Optimization and validation of methods for isolation and realtime PCR identification of protozoan oocysts on leafy green vegetables and berry fruits. Food Waterborne Parasitol. 2016;2:1-7.  https://doi.org/10.1016/j.fawpar.2015.12.002 
  26. Lalonde LF, Gajadhar AA. Detection of Cyclospora cayetanensis, Cryptosporidium spp., and Toxoplasma gondii on imported leafy green vegetables in Canadian survey. Food Waterborne Parasitol. 2016;2:8-14.  https://doi.org/10.1016/j.fawpar.2016.01.001 
  27. European Commission (EC). Food-Based Dietary Guidelines recommendations for vegetables. Brussels: EC; 13 Jan 2025. Available from: https://knowledge4policy.ec.europa.eu/health-promotion-knowledge-gateway/food-based-dietary-guidelines-europe-table-5_en
  28. Moreno-Mesonero L, Soler L, Amorós I, Moreno Y, Ferrús MA, Alonso JL. Protozoan parasites and free-living amoebae contamination in organic leafy green vegetables and strawberries from Spain. Food Waterborne Parasitol. 2023;32:e00200.  https://doi.org/10.1016/j.fawpar.2023.e00200  PMID: 37405064 
  29. Castro-Ibáñez I, Gil MI, Allende A. Ready-to-eat vegetables: Current problems and potential solutions to reduce microbial risk in the production chain. Lebensm Wiss Technol. 2017;85:284-92.  https://doi.org/10.1016/j.lwt.2016.11.073 
  30. Fernández-Escobar M, Schares G, Maksimov P, Joeres M, Ortega-Mora LM, Calero-Bernal R. Toxoplasma gondii genotyping: a closer look into Europe. Front Cell Infect Microbiol. 2022;12:842595.  https://doi.org/10.3389/fcimb.2022.842595  PMID: 35402301 
  31. Castro-Ibáñez I, Gil MI, Allende A. Ready-to-eat vegetables: Current problems and potential solutions to reduce microbial risk in the production chain. Lebensm Wiss Technol. 2017;85:284-92.  https://doi.org/10.1016/j.lwt.2016.11.073 
  32. European Commission (EC). Commission Delegated Regulation (EU) 2023/2429 of 17 August 2023 supplementing Regulation (EU) No 1308/2013 of the European Parliament and of the Council as regards marketing standards for the fruit and vegetables sector, certain processed fruit and vegetable products and the bananas sector, and repealing Commission Regulation (EC) No 1666/1999 and Commission Implementing Regulations (EU) No 543/2011 and (EU) No 1333/2011. EC: Brussels; 3 Nov 2023. Available from: https://eur-lex.europa.eu/legal-content/EN/TXT/PDF/?uri=OJ:L_202302429&qid=1747399302221
  33. Food and Agriculture Organization (FAO) and World Health Organization (WHO). Prevention and control of microbiological hazards in fresh fruits and vegetables – Parts 1 & 2: General principles, No. 42. FAO: Rome; 2023. Available from: https://openknowledge.fao.org/handle/20.500.14283/cc8490en
  34. Calero-Bernal R, Gennari SM, Cano S, Salas-Fajardo MY, Ríos A, Álvarez-García G, et al. Anti-Toxoplasma gondii antibodies in European residents: a systematic review and meta-analysis of studies published between 2000 and 2020. Pathogens. 2023;12(12):1430.  https://doi.org/10.3390/pathogens12121430  PMID: 38133313 
  35. Logar J, Soba B, Premru-Srsen T, Novak-Antolic Z. Seasonal variations in acute toxoplasmosis in pregnant women in Slovenia. Clin Microbiol Infect. 2005;11(10):852-5.  https://doi.org/10.1111/j.1469-0691.2005.01244.x  PMID: 16153265 
  36. Sagel U, Mikolajczyk RT, Krämer A. Seasonal trends in acute toxoplasmosis in pregnancy in the federal state of Upper Austria. Clin Microbiol Infect. 2010;16(5):515-7.  https://doi.org/10.1111/j.1469-0691.2009.02880.x  PMID: 19622079 
  37. Castro-Ibáñez I, López-Gálvez F, Gil MI, Allende A. Identification of sampling points suitable for the detection of microbial contamination in fresh-cut processing lines. Food Control. 2016;59:841-8.  https://doi.org/10.1016/j.foodcont.2015.07.004 
/content/10.2807/1560-7917.ES.2025.30.22.2400594
Loading

Data & Media loading...

Supplementary data

Submit comment
Close
Comment moderation successfully completed
This is a required field
Please enter a valid email address
Approval was a Success
Invalid data
An Error Occurred
Approval was partially successful, following selected items could not be processed due to error