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      The impact of lowering the cut-off value on the sensitivity of the Platelia Elisa IgG (Bio-Rad) test for toxoplasmosis diagnosis Translated title: Impact de la diminution de la valeur du seuil de positivité sur la sensibilité du test Platelia Elisa IgG (Bio-Rad) pour le diagnostic de la toxoplasmose

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          Determining specific immune status against Toxoplasma gondii is essential for assessing the risk of reactivation in immunocompromised patients or defining serological monitoring and appropriate prophylactic measures during pregnancy. In France, toxoplasmosis serological screening requires systematic testing for IgM and IgG antibodies. The Platelia Toxo IgG and IgM test (Bio-Rad) is one of the most widely used tests for anti-toxoplasmic antibody detection. We performed a study on 384 sera, including 123 IgG negative (<6 IU/mL) and 261 IgG equivocal (6–9 IU/mL) sera tested with Platelia Toxo IgG and collected during routine screening at Pitié-Salpêtrière Hospital, Paris, France to determine the best-performing IgG titer cut-off value. Out of these 383 sera, 298 were IgM negative by Platelia Toxo IgM and 86 were IgM positive. All sera were also tested against Toxo IgG II LD BIO western blot test as confirmation. Our results indicated that an IgG titer cut-off value of ≥4.4 IU/mL for the Platelia Toxo IgG met the definition of positivity, a value significantly lower than that indicated by the manufacturers. In the presence of IgM antibodies, the IgG titer cut-off decreased significantly to a value ≥0.2 IU/mL. This latter cut-off also allowed adequate diagnosis of proven toxoplasmosis seroconversion in 76.7% of cases (33/43). Our findings may improve toxoplasmosis care by reducing therapeutic intervention time and eliminating the need for further serological monitoring.

          Translated abstract

          La détermination du statut immunitaire spécifique contre Toxoplasma gondii est essentielle pour évaluer le risque de réactivation chez les patients immunodéprimés ou définir la surveillance sérologique et les mesures prophylactiques appropriées pendant la grossesse. En France, le dépistage sérologique de la toxoplasmose repose sur la mise en évidence des IgG et IgM antitoxoplasmiques. La technique Platelia Toxo IgG (Bio-Rad) est l’un des tests les plus couramment utilisés pour la détection des anticorps anti-toxoplasmose. Nous avons réalisé une étude sur 384 sérums dont 123 étaient IgG négatifs (< 6 UI/mL) et 261 étaient douteux (6–9 UI/mL) avec la technique Platelia Toxo IgG, collectés dans le cadre de l’activité de routine des Hôpitaux Pitié Salpêtrière à Paris, France, afin de déterminer la valeur la plus discriminante du seuil de positivité pour le titre des IgG. Parmi les 384 sérums, 298 étaient IgM négatifs et 86 étaient IgM positifs avec la technique Platelia Toxo IgM. Tous les sérums ont été systématiquement testés en Western Blot avec la trousse LD BIO Toxo IgG II LDBIO utilisée comme test de référence. Nos résultats montrent qu’un titre d’IgG ≥ 4.4 UI/mL pour le Platelia Toxo IgG définit le seuil de positivité de la technique, une valeur nettement inférieure à celle recommandé par le fabricant (9 UI/mL). En présence d’IgM, le seuil de positivité du titre des IgG baisse de manière significative à ≥ 0.2 UI/mL. Ce dernier seuil a permis le diagnostic de 76.7 % (33/43) des séroconversions toxoplasmiques avérées. Nos résultats peuvent améliorer le soin de la toxoplasmose en réduisant la durée des interventions thérapeutiques et en éliminant le besoin de surveillance sérologique supplémentaire.

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          Effect of prenatal treatment on mother to child transmission of Toxoplasma gondii: retrospective cohort study of 554 mother-child pairs in Lyon, France.

          The aim of prenatal serological screening for toxoplasmosis is to identify and treat maternal infection as soon as possible in order to prevent transmission of the parasite to the fetus. However, despite widespread provision of prenatal toxoplasma screening across Europe, the effectiveness of prenatal treatment is uncertain. The study aimed to determine the effect of the timing and type of prenatal treatment on mother to child transmission of Toxoplasma gondii. A cohort of 554 infected pregnant women were identified in Lyon, France between 1987 and 1995 and their children were followed to determine congenital infection status. We determined the effect of prenatal treatment on transmission by examining the effect of the delay between maternal seroconversion and start of treatment. We also compared the effect of the type of treatment and no treatment on the risk of mother to child transmission. Analyses were adjusted for gestation at maternal seroconversion. Compared to treatment within 4 weeks from seroconversion, the adjusted odds ratios (OR) for mother to child transmission after a treatment delay of 4-7 weeks was 1.29 (95% CI : 0.61, 2.73) and after more than 8 weeks, 1.44 (95% CI : 0.60, 3.31). The adjusted OR associated with spiramycin alone compared with pyrimethamine-sulfadiazine treatment was 0.91 (95% CI : 0.45, 1.84) and the OR for no treatment compared with pyrimethamine-sulfadiazine treatment was 1.06 (95% CI : 0.37, 3.03). The authors hypothesize that the absence of an effect of prenatal treatment is due to transmission before the start of treatment.
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            LDBio-Toxo II immunoglobulin G Western blot confirmatory test for anti-toxoplasma antibody detection.

            Tests commonly used for routine determination of anti-Toxoplasma gondii immunoglobulin G (IgG) antibodies show a high level of consistency. However, considerable variations between commercial screening tests are still observed in detecting antibodies present at low concentrations, leading to a number of discrepant and/or equivocal results. It is therefore important to use a reference test to confirm borderline results. In this study, we evaluated the use of a new qualitative test based on Western blot analysis--the LDBio-Toxo II IgG test--as a confirmatory test for at-risk patients. The study was performed retrospectively, using 569 serum samples with "low-positive" (2 to 32 international units) anti-Toxoplasma IgG levels from 375 patients. These samples were either sera collected during the routine screening of pregnant women, from patients with unrelated infections, or from immunocompromised patients or sequential sera taken from pregnant women with acquired Toxoplasma infection or from their newborns during follow-up. The LDBio-Toxo II IgG test was compared to several commercial tests commonly used for anti-Toxoplasma IgG screening. The Sabin-Feldman dye test was used as a reference test. In this study, the results of the LDBio-Toxo II IgG test appeared to be consistent with those of the dye test; the LDBio-Toxo II IgG test had a specificity of 100% and a sensitivity of 99.2%. Our findings suggest that the LDBio-Toxo II IgG test is a useful serological tool in cases in which the presence or absence of Toxoplasma antibodies needs to be reliably determined, for example, for the follow-up of pregnant women and their newborns or for subjects with immune deficiencies following human immunodeficiency virus infection, hematological malignancies, or transplantation.
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              Discrepancies between a new highly sensitive Toxoplasma gondii ELISA assay and other reagents: interest of Toxo IgG Western blot.

              Immunodiagnostic assays are commonly used to screen for maternal toxoplasmic seroconversion during pregnancy. The introduction to the market of a new highly sensitive IgG assay, the Elecsys Toxo IgG test, has resulted in discrepancy issues with other immunoassays because of a lack of standardisation. Western blot appears to be a good alternative gold standard to the dye test, as the latter is not routinely available. For the present prospective study, we compared the analytical performances of two immunoassays, Elecsys Toxo IgG (Roche Diagnostics) and Platelia Toxo IgG (Bio-Rad, Marnes la Coquette, France), to Toxo II IgG Western blot (LDBio, Lyon, France) using 231 consecutive sera with low or equivocal IgG titres. Of these 231 sera, 213 presented discrepancies, which showed the importance of a confirmation test. Of the Elecsys Toxo IgG-positive results, 100% were confirmed by the Western blot with a positive threshold of 30 IU/ml for Elecsys; in the equivocal area (1-30 IU/ml), Western blot is negative in 54% of cases. Our results suggest that the lower diagnostic cut-off of Platelia Toxo IgG should be further reduced. Our study indirectly confirms that monitoring, especially for pregnant women, must be done in the same laboratory using the same technique. The ability to diagnose very early seroconversion using Western blot merits further study.

                Author and article information

                EDP Sciences
                17 July 2015
                : 22
                : ( publisher-idID: parasite/2015/01 )
                [1 ] AP-HP, Groupe Hospitalier La Pitié-Salpêtrière, Service de Parasitologie-Mycologie 75013 Paris France
                [2 ] Centre d’Immunologie et des Maladies Infectieuses, CIMI-Paris 75013 Paris France
                [3 ] Sorbonne Universités, UPMC Université Paris 6, CIMI-Paris 75005 Paris France
                Author notes

                Both authors with equal contributions to this paper.

                [* ]Corresponding author: oussama.mouri@ 123456psl.aphp.fr
                parasite150005 10.1051/parasite/2015022
                © O. Mouri et al., published by EDP Sciences, 2015

                This is an Open Access article distributed under the terms of the Creative Commons Attribution License ( http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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                Figures: 4, Tables: 0, Equations: 0, References: 11, Pages: 6
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