The adoption of a point-of-care (POC) test to detect Toxoplasma gondii infection would substantially reduce costs and require significantly less infrastructure than conventional testing, according to a study published in PLoS One Neglected Tropical Diseases.
Infection with T gondii can be severe, causing substantial morbidity and mortality on a global scale. Primary acute infection during pregnancy can result in vertical transmission from mother to fetus; subsequent congenital infection may result in chorioretinitis, hydrocephalus, epilepsy, and death. Serologic screening during gestation allows early antenatal detection and rapid treatment initiation; however, conventional serologic screening can be cost-prohibitive and infrastructure, including electricity and equipment for sample processing, may not be available. POC tests detecting T gondii infection could potentially markedly change the clinical approach to this infection by detecting seroconversion using small volumes of whole blood. Therefore, this study tested whether a comparably performing small volume whole-blood-variant test, which would obviate the need for venipuncture and sample processing infrastructure, could make an efficient low-cost POC test that performs with high sensitivity and specificity.
Samples were obtained from consenting US individuals, including seropositive individuals affiliated with the National Collaborative Chicago-Based Congenital Toxoplasmosis Study (NCCCTS) and obstetrical patients in Chicago and Morocco. A total of 205 participants (244 samples) had their serologic status for T gondii assessed using the whole blood-variant test and confirmed using their NCCCTS records (n=71) or concurrent standard laboratory testing (n=134).
Seropositive was defined as having detectable anti-Toxoplasma IgG and/or IgM. Of all samples, 101 proved seropositive, including 5 from acutely infected individuals who had IgM/IgG antibodies against T gondii, while 143 were seronegative. The whole-blood test proved highly sensitive and specific, with a sensitivity of 100% (95% CI, 96.41%-100%) and specificity of 100% (95% CI, 97.45%-100%). In addition, whole-blood, serum-variant, and reference testing demonstrated 100% concordance. Further, individuals with lower levels of anti-Toxoplasma antibodies who were infected at remote times and with lower titers were positive on the POC test in the range detected by gold-standard tests. The fingerstick aspect of the test proved to be a feasible testing modality as no patient refused a second fingerstick although they were told they could, and did not report significant discomfort. This POC test cannot distinguish IgG and IgM seropositivity and therefore cannot distinguish acute from chronic infection.
Overall, the researchers concluded that, “Ultimately, [this fingerstick] is an accurate, well-validated POC testing, rather than a specific company’s test, that can reduce morbidity and mortality from congenital toxoplasmosis and most benefit patients and their families.”
Lykins J, Li X, Levigne P, Zhou Y, et al. Rapid, inexpensive, fingerstick, whole-blood, sensitive, specific, point-of-care test for anti-Toxoplasma antibodies. [published online August 16, 2018] Plos Negl Trop Dis. doi:10.1371/journal.pntd.0006536