The performance of four molecular methods for the laboratory diagnosis of congenital toxoplasmosis in amniotic fluid samples

Author(s)

Teixeira, Leandro Emidio ^[1] ; Kanunfre, Kelly Aparecida ^{[1, 2]} ; Shimokawa, Paulo Tadashi ^[1] ; Targa, Lilia Spaleta ^[1] ; Rodrigues, Jonatas Cristian ^{[1, 2]} ; Domingues, Wilson ^[1] ; Yamamoto, Lidia ^[1] ; Okay, Thelma Suely ^[1]

Affiliation

^[1] Univ Sao Paulo, Inst Med Trop Sao Paulo, Lab Soroepidemiol & Imunobiol, Sao Paulo - Brazil

^[2] Univ Sao Paulo, Fac Med, Dept Doencas Infecciosas & Parasitarias, Lab Imunol, Sao Paulo - Brazil

• Document type: Journal article
• Source: Revista da Sociedade Brasileira de Medicina Tropical; v. 46, n. 5, p. 584-588, SEP-OCT 2013.
• Web of Science Citations: 14

Abstract

Introduction: Toxoplasmosis may be life-threatening in fetuses and in immune-deficient patients. Conventional laboratory diagnosis of toxoplasmosis is based on the presence of IgM and IgG anti-Toxoplasma gondii antibodies; however, molecular techniques have emerged as alternative tools due to their increased sensitivity. The aim of this study was to compare the performance of 4 PCR-based methods for the laboratory diagnosis of toxoplasmosis. One hundred pregnant women who seroconverted during pregnancy were included in the study. The definition of cases was based on a 12-month follow-up of the infants. Methods: Amniotic fluid samples were submitted to DNA extraction and amplification by the following 4 Toxoplasma techniques performed with parasite B1 gene primers: conventional PCR, nested-PCR, multiplex-nested-PCR, and real-time PCR. Seven parameters were analyzed, sensitivity (Se), specificity (Sp), positive predictive value (PPV), negative predictive value (NPV), positive likelihood ratio (PLR), negative likelihood ratio (NLR) and efficiency (Ef). Results: Fifty-nine of the 100 infants had toxoplasmosis; 42 (71.2%) had IgM antibodies at birth but were asymptomatic, and the remaining 17 cases had non-detectable IgM antibodies but high IgG antibody titers that were associated with retinochoroiditis in 8 (13.5%) cases, abnormal cranial ultrasound in 5 (8.5%) cases, and signs/symptoms suggestive of infection in 4 (6.8%) cases. The conventional PCR assay detected 50 cases (9 false-negatives), nested-PCR detected 58 cases (1 false-negative and 4 false-positives), multiplex-nested-PCR detected 57 cases (2 false-negatives), and real-time-PCR detected 58 cases (1 false-negative). Conclusions: The real-time PCR assay was the best-performing technique based on the parameters of Se (98.3%), Sp (100%), PPV (100%), NPV (97.6%), PLR (co), NLR (0.017), and Ef (99%). (AU)

• FAPESP's process: 10/15022-1 - Frequency of HLA-DQA1 and DQB1 alleles in fetuses with toxoplasmosis: association with the parasite genotype and the parasite load
• Grantee: Thelma Suely Okay
• Support Opportunities: Regular Research Grants