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Clinical and Vaccine Immunology, March 2007, p. 239-243, Vol. 14, No. 3
1071-412X/07/$08.00+0 doi:10.1128/CVI.00311-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Hospices Civils de Lyon, Hôpital de la Croix-Rousse, Service de Parasitologie, Lyon F-69317, France,1 Hospices Civils de Lyon, Service de Biostatistique, Lyon F-69003, France; CNRS, UMR 5558 Equipe Biostatistique-Santé, Villeurbanne F-69100, France; and Université Lyon 1, UMR 5558 Laboratoire Biostatistique-Santé, Villeurbanne F-69100, France,2 Laboratoire de Parasitologie, Mycologie Médicale et Pathologie Exotique, Equipe d'Accueil EA 3732, Université Lyon 1, UFR Médecine Lyon Nord, Lyon, France,3 Hospices Civils de Lyon, Centre Hospitalier Lyon-Sud, Laboratoire d'Immunologie, Pierre-Bénite F-69495, France4
Received 30 August 2006/ Returned for modification 13 October 2006/ Accepted 18 December 2006
The objective of the present study was to investigate the maturation of immunoglobulin G (IgG) avidity after Toxoplasma gondii seroconversion during pregnancy and the factors that affect IgG avidity over time. The study used 309 serum samples from 117 women and a multiple linear mixed regression analysis to show the patterns of variation of IgG avidity throughout gestation. The IgG avidity ratios and the patterns of their evolution with time were quite diverse among the women and were statistically heterogeneous (P = 0.011); however, the trend was toward a statistically significant increase (P < 0.0001). On average, a 1.0167-fold increase was observed for each additional gestational week after the putative date of infection. At 12 weeks after putative infection (the expected IgG avidity maturation time), the mean avidity ratio was 16.6% (95% confidence interval, 15.4 to 17.9%). At all times, the avidity ratio remained significantly heterogeneous among the women (P < 0.05); for 95% of them, that ratio ranged from 7.8 to 35.3% at 12 weeks after putative infection. Maternal age at the putative time of infection did not influence the maturation of IgG avidity. However, on average, a 1.009-fold decrease (P = 0.03) in that avidity was observed for each additional week of gestational age before infection and a 1.03-fold increase (P = 0.0003) was observed for each additional week of delay to the onset of spiramycin treatment. The rate of increase in the avidity ratio was lower if infection occurred late in pregnancy and higher if the delay to treatment was long. This information cannot allow accurate determination of the delay since the time of infection. The present results provide support for interpretation of the assay and caution against overinterpretation.
Published ahead of print on 3 January 2007.
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