Molecular detection of Toxoplasma gondii in ready-to-eat salad mixes: multi-country survey using a validated and harmonised standard operating procedure, Europe, 2021 to 2022
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2025
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European Centre for Disease Prevention and Control
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Calero-Bernal Rafael, Betson Martha, Slana Iva, Bartosova Barbora, Marucci Gianluca, Possenti Alessia, Álvarez-García Gema, Bier Nadja, Mayer-Scholl Anne, Berg Rebecca P, Chaudhry Umer, López-Ureña Nadia M, Piotrowska Weronika, Sroka Jacek, Johannessen Gro S, Davidson Rebecca, Dámek Filip, Blaga Radu, Thoumire Sandra, Zalewská Barbora, Waap Helga C, Jokelainen Pikka, Lalle Marco. Molecular detection of Toxoplasma gondii in ready-to-eat salad mixes: multicountry survey using a validated and harmonised standard operating procedure, Europe, 2021 to 2022. Euro Surveill. 2025;30(22):pii=2400594. https://doi. org/10.2807/1560-7917.ES.2025.30.22.2400594
Abstract
Background: Most Toxoplasma gondii 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 T. gondii oocysts has been identified as a possible source. Aim: We aimed to estimate the occurrence and prevalence of T. gondii oocysts in commercially available ready-to-eat (RTE) salad mixes in 10 European countries. Methods: A real-time PCRbased 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 multicountry 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 T. gondii 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 T. gondii, with no statistically significant differences between salad types. Conclusion: We estimated the prevalence of T. gondii 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
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Authors’ contributions:
ML, NB, MB, RCB, GAG conceived and designed the study; ML, GM, IS, BB coordinated and performed methodology development; and preparation of video; ML, GM coordinated interlaboratory test performance and data acquisition; ML, RCB, GAG, NLU, MB, GM, AP, NB, AMS, RPB, UC, WP, JS, GJ, RD, FD, RB, ST, BZ, HW, PJ carried out sample collection and preparation; RCB, UC, AP, GM, RPB, NLU, WP, GJ, FD, ST, BZ carried out molecular detection and results interpretation; RCB, NLU performed confirmatory assays; MB, ML did statistical analyses; ML, RCB, GAG, MB drafted the manuscript; ML, RCB, GAG, MB, PJ, RB, RPB corrected the manuscript; all authors approved the final version. ML, PJ acquired funding for the study.