Evaluation of Three Point-of-Care Tests for Detection of Toxoplasma Immunoglobulin IgG and IgM in the United States: Proof of Concept and Challenges

Carlos A Gomez; Laura N Budvytyte; Cindy Press; Lily Zhou; Rima McLeod; Yvonne Maldonado; Jose G Montoya; Despina G Contopoulos-Ioannidis

doi:10.1093/ofid/ofy215

Evaluation of Three Point-of-Care Tests for Detection of Toxoplasma Immunoglobulin IgG and IgM in the United States: Proof of Concept and Challenges

Open Forum Infect Dis. 2018 Oct 29;5(10):ofy215. doi: 10.1093/ofid/ofy215. eCollection 2018 Oct.

Authors

Carlos A Gomez^{1

2}, Laura N Budvytyte^{1

2}, Cindy Press², Lily Zhou², Rima McLeod³, Yvonne Maldonado⁴, Jose G Montoya^{1

2}, Despina G Contopoulos-Ioannidis⁴

Affiliations

¹ Division of Infectious Diseases and Geographic Medicine, Department of Medicine, Stanford University School of Medicine, California.
² Palo Alto Medical Foundation Toxoplasma Serology Laboratory, National Reference Center for the Study and Diagnosis of Toxoplasmosis, California.
³ Toxoplasmosis Center, Department of Pediatrics, Division of Infectious Diseases, Ophthalmology and Visual Sciences, University of Chicago, Illinois.
⁴ Department of Pediatrics, Division of Infectious Diseases, Stanford University School of Medicine, California.

Abstract

Background: The cost of conventional serological testing for toxoplasmosis discourages universal adoption of prenatal monthly screening programs to prevent congenital toxoplasmosis. Point-of-care (POC) technology may constitute a cost-effective approach.

Methods: We evaluated the diagnostic accuracy of 3 Toxoplasma POC tests against gold-standard testing performed at Palo Alto Medical Foundation Toxoplasma Serology Laboratory (PAMF-TSL). The POC tests included the following: Toxo IgG/IgM Rapid Test (Biopanda) and the OnSite Toxo IgG/IgM Combo-Rapid-test that detect IgG and IgM separately, and the Toxoplasma ICT-IgG-IgM-bk (LDBIO) that detects either or both immunoglobulin IgG/IgM in combination. Samples were selected from PAMF-TSL biobank (n = 210) and Centers for Disease Control and Prevention Toxoplasma 1998 Human Serum Panel (n = 100). Based on PAMF-TSL testing, Toxoplasma-infection status was classified in 4 categories: acute infections (n = 85), chronic infections (n = 85), false-positive Toxoplasma IgM (n = 60), and seronegative (n = 80). The POC testing was performed in duplicate following manufacturer's instructions by investigators blinded to PAMF-TSL results. Sensitivity and specificity were calculated.

Results: A total of 1860 POC tests were performed. For detection of Toxoplasma IgG, sensitivity was 100% (170 of 170; 95% confidence interval [CI], 97.8%-100%) for all 3 POC kits; specificity was also comparable at 96.3% (77 of 80; 95% CI, 89.5%-98.9%), 97.5% (78 of 80; 95% CI, 91.3%-99.6%), and 98.8% (79 of 80; 95% CI, 93.2%-99.9%). However, sensitivity for detection of Toxoplasma IgM varied significantly across POC tests: Biopanda, 62.2% (51 of 82; 95% CI, 51.4%-71.9%); OnSite, 28% (23 of 82; 95% CI, 19.5%-38.6%); and LDBIO combined IgG/IgM, 100% (82 of 82; 95% CI, 95.5%-100%). Diagnostic accuracy was significantly higher for the LDBIO POC kit. The POC kits did not exhibit cross-reactivity for false-positive Toxoplasma-IgM sera.

Conclusions: The 3 evaluated POC kits revealed optimal sensitivity for Toxoplasma-IgG antibodies. The LDBIO-POC test exhibited 100% sensitivity for the combined detection of IgG/IgM in acute and chronic Toxoplasma infection. Biopanda and Onsite POC tests exhibited poor sensitivity for Toxoplasma-IgM detection.

Keywords: Toxoplasma gondii; immunoglobulin G; immunoglobulin M; point-of-care testing; toxoplasmosis.