{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,4,3]],"date-time":"2026-04-03T06:09:23Z","timestamp":1775196563895,"version":"3.50.1"},"reference-count":43,"publisher":"Public Library of Science (PLoS)","issue":"4","license":[{"start":{"date-parts":[[2023,4,13]],"date-time":"2023-04-13T00:00:00Z","timestamp":1681344000000},"content-version":"vor","delay-in-days":0,"URL":"http:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/501100003243","name":"Ministerstvo Zdravotnictv\u00ed Cesk\u00e9 Republiky","doi-asserted-by":"publisher","award":["MZDR\/11034\/2021-17\/VLP"],"award-info":[{"award-number":["MZDR\/11034\/2021-17\/VLP"]}],"id":[{"id":"10.13039\/501100003243","id-type":"DOI","asserted-by":"publisher"}]},{"DOI":"10.13039\/501100007601","name":"Horizon 2020","doi-asserted-by":"publisher","award":["773830"],"award-info":[{"award-number":["773830"]}],"id":[{"id":"10.13039\/501100007601","id-type":"DOI","asserted-by":"publisher"}]}],"content-domain":{"domain":["www.plosone.org"],"crossmark-restriction":false},"short-container-title":["PLoS ONE"],"abstract":"<jats:sec id=\"sec001\">\n<jats:title>Objectives<\/jats:title>\n<jats:p>For the proper diagnosis of toxoplasmosis it is essential to determine the stage of the infection, for which the most preferred method is IgG avidity test. The avidity index (AI) should initially be low (AI\u22640.3) in the acute phase and increase during the infection. However, persistent low avidity can occur in patients with latent toxoplasmosis, which can complicate the interpretation of the results. The aim of the study is to explain the causes of this phenomenon.<\/jats:p>\n<\/jats:sec>\n<jats:sec id=\"sec002\">\n<jats:title>Methodology<\/jats:title>\n<jats:p>A retrospective study was carried out with 717 serum samples collected from 442 patients from the categories of pregnant and non-pregnant women, men, and newborns + infants (age &lt; 0.5 year). The trends of AI kinetics were evaluated in repeatedly examined patients. The frequency of cases with low avidity was compared in individual categories of patients and in groups of people with acute and non-acute toxoplasmosis.<\/jats:p>\n<\/jats:sec>\n<jats:sec id=\"sec003\">\n<jats:title>Results<\/jats:title>\n<jats:p>The proportion of patients with initially low avidity was 42.1% in the acute toxoplasmosis group while it was 13.0% in the non-acute groups. In uninfected newborns with anti-<jats:italic>Toxoplasma<\/jats:italic> antibodies transmitted from the mother, a decrease in IgG avidity levels over time was observed, resulting in 29.2% of samples showing low (improper) avidity. While the dynamics of IgG avidity and the frequency of cases of improperly low avidity were similar in men and pregnant and non-pregnant women, the category of newborns and infants differed substantially for these indicators.<\/jats:p>\n<\/jats:sec>\n<jats:sec id=\"sec004\">\n<jats:title>Conclusions<\/jats:title>\n<jats:p>Due to acceptable specificity and negative predictive value, high avidity can rule out acute toxoplasmosis, but moderate sensitivity complicates the possibility of its confirmation. The results of the avidity test must be interpreted in the context of the results of other methods.<\/jats:p>\n<\/jats:sec>","DOI":"10.1371\/journal.pone.0284499","type":"journal-article","created":{"date-parts":[[2023,4,13]],"date-time":"2023-04-13T18:23:24Z","timestamp":1681410204000},"page":"e0284499","update-policy":"https:\/\/doi.org\/10.1371\/journal.pone.corrections_policy","source":"Crossref","is-referenced-by-count":9,"title":["Detection of persistent low IgG avidity\u2013an interpretative problem in the diagnosis of acute toxoplasmosis"],"prefix":"10.1371","volume":"18","author":[{"ORCID":"https:\/\/orcid.org\/0000-0003-2437-8617","authenticated-orcid":true,"given":"Petr","family":"Kodym","sequence":"first","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Zuzana","family":"Kurzov\u00e1","sequence":"additional","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Dagmar","family":"Berenov\u00e1","sequence":"additional","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Marek","family":"Mal\u00fd","sequence":"additional","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"340","published-online":{"date-parts":[[2023,4,13]]},"reference":[{"key":"pone.0284499.ref001","first-page":"356","volume-title":"In Immunology of parasitic infections","author":"JL Krahenbuhl","year":"1982","edition":"2"},{"key":"pone.0284499.ref002","first-page":"163","volume-title":"Parasitic infections and the immune system","author":"F Darcy","year":"1990"},{"key":"pone.0284499.ref003","doi-asserted-by":"crossref","first-page":"111","DOI":"10.1007\/978-2-8178-0847-5_8","volume-title":"Congenital toxoplasmosis: Scientific background, clinical management and control","author":"F. Jacquemard","year":"2000"},{"key":"pone.0284499.ref004","first-page":"121","volume-title":"Congenital toxoplasmosis. Scientific Background, Clinical Management and Control","author":"U Gross","year":"2000"},{"issue":"4","key":"pone.0284499.ref005","doi-asserted-by":"crossref","first-page":"736","DOI":"10.1093\/infdis\/159.4.736","article-title":"Recent primary toxoplasma infection indicated by a low avidity of specific IgG","volume":"159","author":"K Hedman","year":"1989","journal-title":"J Infect Dis"},{"key":"pone.0284499.ref006","doi-asserted-by":"crossref","first-page":"123","DOI":"10.1097\/00013542-199307000-00001","article-title":"Avidity of IgG in serodiagnosis of infectious diseases.","volume":"4","author":"K Hedman","year":"1993","journal-title":"Rev. Med. Microbiol"},{"issue":"4","key":"pone.0284499.ref007","doi-asserted-by":"crossref","first-page":"511","DOI":"10.1517\/17530059.1.4.511","article-title":"Clinical utility of avidity assays.","volume":"1","author":"SL Hazell","year":"2007","journal-title":"Expert Opin Med Diagn"},{"issue":"9","key":"pone.0284499.ref008","doi-asserted-by":"crossref","first-page":"e00505","DOI":"10.1128\/JCM.00505-20","article-title":"Role of Toxoplasma gondii IgG avidity testing in discriminating between acute and chronic toxoplasmosis in pregnancy","volume":"58","author":"A Teimouri","year":"2020","journal-title":"J Clin Microbiol"},{"issue":"8","key":"pone.0284499.ref009","doi-asserted-by":"crossref","first-page":"1972","DOI":"10.1128\/jcm.35.8.1972-1977.1997","article-title":"Improved diagnosis of primary Toxoplasma gondii infection in early pregnancy by determination of antitoxoplasma immunoglobulin G avidity","volume":"35","author":"PA Jenum","year":"1997","journal-title":"J Clin Microbiol"},{"key":"pone.0284499.ref010","doi-asserted-by":"crossref","first-page":"61","DOI":"10.1016\/j.jim.2017.08.010","article-title":"Proposed panel of diagnostic tools for accurate temporal classification of symptomatic T. gondii infection","volume":"451","author":"GB Barros","year":"2017","journal-title":"J Immunol Methods"},{"issue":"11","key":"pone.0284499.ref011","doi-asserted-by":"crossref","first-page":"687","DOI":"10.1007\/s10096-006-0204-1","article-title":"Delayed maturation of immunoglobulin G avidity: implication for the diagnosis of toxoplasmosis in pregnant women","volume":"25","author":"M Lefevre-Pettazzoni","year":"2006","journal-title":"Eur J Clin Microbiol Infect Dis"},{"issue":"3","key":"pone.0284499.ref012","doi-asserted-by":"crossref","first-page":"249","DOI":"10.1556\/EuJMI.1.2011.3.9","article-title":"Antiparasitic treatment suppresses production and avidity of Toxoplasma gondii-specific antibodies in a murine model of acute infection","volume":"1","author":"C Alvarado-Esquivel","year":"2011","journal-title":"Eur J Microbiol Immunol (Bp)"},{"issue":"1","key":"pone.0284499.ref013","first-page":"127","article-title":"A tween-ether preparation of Toxoplasma gondii antigen for the complement fixation test","volume":"46","author":"J Pokorn\u00fd","year":"1972","journal-title":"Bull. World Health Organ"},{"issue":"suppl. 3","key":"pone.0284499.ref014","first-page":"3","article-title":"Dopln\u011bk standardn\u00edch metodik laboratorn\u00ed diagnostiky toxoplasm\u00f3zy. [Amendment to standard laboratory methods for diagnosing toxoplasmosis\u2014in Czech]","author":"M Z\u00e1st\u011bra","year":"1987","journal-title":"Acta Hyg. Epidemiol. Microbiol"},{"issue":"6","key":"pone.0284499.ref015","first-page":"189","article-title":"The significance of complement fixation test in clinical diagnosis of toxoplasmosis","volume":"104","author":"F Ondriska","year":"2003","journal-title":"Bratisl. Lek. Listy"},{"issue":"1","key":"pone.0284499.ref016","doi-asserted-by":"crossref","first-page":"25","DOI":"10.1111\/j.1469-0691.1996.tb00196.x","article-title":"IgG avidity in the serodiagnosis of acute Toxoplasma gondii infection: a multicenter study","volume":"2","author":"A Sensini","year":"1996","journal-title":"Clin Microbiol Infect"},{"issue":"12","key":"pone.0284499.ref017","doi-asserted-by":"crossref","first-page":"e0145519","DOI":"10.1371\/journal.pone.0145519","article-title":"Persistent Low Toxoplasma IgG Avidity Is Common in Pregnancy: Experience from Antenatal Testing in Norway.","volume":"10","author":"G Findal","year":"2015","journal-title":"PLoS One."},{"issue":"11","key":"pone.0284499.ref018","doi-asserted-by":"crossref","first-page":"825","DOI":"10.1007\/s10096-004-1226-1","article-title":"Delayed maturation of IgG avidity in congenital toxoplasmosis","volume":"23","author":"W Buffolano","year":"2004","journal-title":"Eur J Clin Microbiol Infect Dis"},{"issue":"1","key":"pone.0284499.ref019","first-page":"25","article-title":"Evaluation of the avidity test for the follow up on children treated for congenital toxoplasmosis during the first year of life.","volume":"34","author":"JD Caro-Garz\u00f3n","year":"2021","journal-title":"Itreia"},{"issue":"12","key":"pone.0284499.ref020","doi-asserted-by":"crossref","first-page":"887","DOI":"10.1055\/s-0041-1740272","article-title":"IgG avidity in samples collected on filter paper: Importance of the early diagnosis of congenital toxoplasmosis.","volume":"43","author":"JY Souza","year":"2021","journal-title":"Rev Bras Ginecol Obstet"},{"issue":"2","key":"pone.0284499.ref021","doi-asserted-by":"crossref","first-page":"26","DOI":"10.3390\/pathogens6020026","article-title":"IgG avidity test in congenital toxoplasmosis diagnoses in newborns.","volume":"6","author":"ZC Fonseca","year":"2017","journal-title":"Pathogens"},{"issue":"10","key":"pone.0284499.ref022","doi-asserted-by":"crossref","first-page":"1517","DOI":"10.1128\/CVI.00253-09","article-title":"Spiramycin treatment of Toxoplasma gondii infection in pregnant women impairs the production and the avidity maturation of T. gondii-specific immunoglobulin G antibodies","volume":"16","author":"V Meroni","journal-title":"Clin Vaccine Immunol. 2009"},{"issue":"3","key":"pone.0284499.ref023","doi-asserted-by":"crossref","first-page":"239","DOI":"10.1128\/CVI.00311-06","article-title":"Impact of spiramycin treatment and gestational age on maturation of Toxoplasma gondii immunoglobulin G avidity in pregnant women","volume":"14","author":"M Lefevre-Pettazzoni","journal-title":"Clin Vaccine Immunol. 2007"},{"key":"pone.0284499.ref024","first-page":"56","author":"DO Ho-Yen","year":"1992"},{"key":"pone.0284499.ref025","first-page":"140","volume-title":"Infectious diseases of the foetus and newborn infant","author":"JS Remington","year":"1995","edition":"4"},{"issue":"2","key":"pone.0284499.ref026","doi-asserted-by":"crossref","first-page":"763","DOI":"10.1007\/s00436-020-07022-6","article-title":"PCR-based diagnosis is not always useful in the acute acquired toxoplasmosis in immunocompetent individuals","volume":"120","author":"ES Neves","year":"2021","journal-title":"Parasitol Res"},{"key":"pone.0284499.ref027","first-page":"138","article-title":"Zamy\u0161len\u00ed nad \"postaven\u00edm\" metody PCR v rutinn\u00ed diagnostice toxoplazm\u00f3zy p\u0159i vy\u0161et\u0159en\u00ed perifern\u00ed krve u imunokompetentn\u00edch nemocn\u00fdch.","volume":"15","author":"Z \u010cerm\u00e1kov\u00e1","year":"2009","journal-title":"[Considering the role of the PCR method in routine diagnosis of toxoplasmosis in peripheral blood tests in immunocompetent patients\u2014in Czech]. 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Lek"},{"issue":"2","key":"pone.0284499.ref028","doi-asserted-by":"crossref","first-page":"253","DOI":"10.1007\/s10096-018-3421-5","article-title":"Interpretation of very low avidity indices acquired with the Liaison XL Toxo IgG avidity assay in dating toxoplasmosis infection","volume":"38","author":"F Boquel","year":"2018","journal-title":"Eur J Clin Microbiol Infect Dis"},{"key":"pone.0284499.ref029","doi-asserted-by":"crossref","first-page":"69","DOI":"10.1007\/978-2-8178-0847-5_5","volume-title":"Congenital toxoplasmosis: Scientific background, clinical management and control","author":"J Alexander","year":"2000"},{"issue":"1","key":"pone.0284499.ref030","doi-asserted-by":"crossref","first-page":"40","DOI":"10.1111\/j.1469-0691.2006.01564.x","article-title":"Evaluation of a commercial IgE ELISA in comparison with IgA and IgM ELISAs, IgG avidity assay and complement fixation for the diagnosis of acute toxoplasmosis","volume":"13","author":"P Kodym","year":"2007","journal-title":"Clin Microbiol Infect"},{"issue":"5","key":"pone.0284499.ref031","doi-asserted-by":"crossref","first-page":"487","DOI":"10.3347\/kjp.2014.52.5.487","article-title":"IgG avidity antibodies against Toxoplasma gondii in high risk females of reproductive age group in India.","volume":"52","author":"N Siddiqui","year":"2014","journal-title":"Korean J Parasitol"},{"issue":"4","key":"pone.0284499.ref032","first-page":"251","article-title":"IgG avidity test for the diagnosis of acute Toxoplasma gondii infection in early pregnancy","volume":"8","author":"SP Abolghasem","year":"2011","journal-title":"Iran J Immunol"},{"issue":"8","key":"pone.0284499.ref033","doi-asserted-by":"crossref","first-page":"1248","DOI":"10.1086\/319672","article-title":"Effect of testing for IgG avidity in the diagnosis of Toxoplasma gondii infection in pregnant women: experience in a US reference laboratory","volume":"183","author":"O Liesenfeld","journal-title":"J Infect Dis. 200;"},{"issue":"6","key":"pone.0284499.ref034","doi-asserted-by":"crossref","first-page":"492","DOI":"10.1016\/j.pt.2016.04.001","article-title":"Relevance of and new developments in serology for Toxoplasmosis","volume":"32","author":"C Dard","year":"2016","journal-title":"Trends Parasitol"},{"issue":"4","key":"pone.0284499.ref035","doi-asserted-by":"crossref","first-page":"1570","DOI":"10.1128\/JCM.43.4.1570-1574.2005","article-title":"European multicenter study of the LIAISON automated diagnostic system for determination of Toxoplasma gondii-specific immunoglobulin G (IgG) and IgM and the IgG avidity index.","volume":"43","author":"E Petersen","year":"2005","journal-title":"J Clin Microbiol"},{"issue":"4","key":"pone.0284499.ref036","first-page":"669","article-title":"Reliability of immunoglobulin G antitoxoplasma avidity test and effects of treatment on avidity indexes of infants and pregnant women","volume":"11","author":"P Flori","year":"2004","journal-title":"Clin Diagn Lab 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