Impact of Spiramycin Treatment and Gestational Age on Maturation ofToxoplasma gondiiImmunoglobulin G Avidity in Pregnant Women

Abstract

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.Acute Toxoplasma gondii infection can have serious consequences on fetal development, including abortion, neurological and ocular fetal lesions, and subclinical infections (26). Moreover, some toxoplasma-linked ocular lesions appear or relapse during childhood or adolescence (25,33). This is why, in France, a monthly serological follow-up during pregnancy has been mandatory for seronegative women since 1992 (32).The risk of mother-to-child transmission of Toxoplasma gondii was shown to be inversely proportional to the stage of pregnancy at which maternal infection occurs (9, 17). Thus, dating of maternal toxoplasma infection during pregnancy is of great importance because it allows determination of the fetal risk. Today, various serological markers may be used to estimate the time that has elapsed since Toxoplasma seroconversion, including measurement of immunoglobulin G (IgG) avidity (16). Although it is well recognized that a high IgG avidity ratio can rule out acute infection, a low IgG avidity ratio is insufficient to infer a recent infection (21). Moreover, data on the evolution of the IgG avidity ratio over time after Toxoplasma infection are lacking. Although the heterogeneity of that evolution has already been reported (13), studies on the effect of ...

A hepatitis C avidity test for determining recent and past infections in both plasma and dried blood spots

“…15,16 Many factors have been found to influence the progression from low to high avidity. [23][24][25][26] A low avidity result with the assay described in this paper suggested that a recent HCV infection has occurred within ∼4-5 months. In this study, group 1 (acute patients) were defined as becoming anti-HCV positive after a previous negative result taken 4-6 months ago.…”

Epidemiology of and Diagnostic Strategies for Toxoplasmosis

“…However, when the avidity index is low or intermediate, the interpretation is ambivalent, since it cannot exclude an infection acquired in the preceding 4 months but also cannot prove that it is recent, unless the index is extremely low. From this standpoint, it should be kept in mind that treatment delays IgG avidity maturation (202). In a study by Petersen et al (253), the mean IgG avidity index determined during the 16 weeks following infection was lower in treated pregnant women than in untreated nonpregnant patients (0.092 versus 0.149; P Ͻ 0.01).…”

“…Another way to appreciate the age of infection resides in the kinetics of IgG titers analyzed in two serum samples obtained at 3-week intervals in the absence of any specific therapy. Rising IgG titers are suggestive of an infection acquired less than 2 months before the earlier sample, but one must be aware that treatment may also reduce or abolish the increase of IgG titers (202). Combinations of different diagnostic tools and clear-cut interpretations are necessary to achieve an accurate dating of infection and safe counseling for pregnancy management (Fig.…”

Help in the Choice of Automated or Semiautomated Immunoassays for Serological Diagnosis of Toxoplasmosis: Evaluation of Nine Immunoassays by the French National Reference Center for Toxoplasmosis

“…When such a scenario is observed in pregnant women, this leads us to consider the possibility of a recent infection, rendering it essential to confirm this infection before implementing a treatment designed to decrease fetal transmission and involvement (51,52). The AxSYM and Elecsys IgG assays were found to be the most efficient methods in the patients in whom a seroconversion was assessed (Tables 5 and 6).…”