Chagas disease serological test performance in United States blood donor specimens

Abstract

25Background: Chagas disease affects an estimated 300,000 individuals in the US. Diagnosis in 26 the chronic phase requires positive results by two different IgG serological tests. Three ELISAs 27(Hemagen, Ortho, Wiener) and one rapid test (InBios) are FDA-cleared, but comparative data in 28 US populations are sparse. 30Methods: We evaluated 500 seropositive and 300 seronegative blood donor plasma samples. 31Country of birth was known for 255 seropositive specimens and grouped into regions: Mexico 32 (n=94), Central America (n=88) and South America (n=73). Specimens were tested by the four 33 FDA-cleared IgG serological assays. Test performance was evaluated by two comparators and 34 latent class analysis. 36Results: InBios had the highest sensitivity (97.4-99.3%), but lowest specificity (87.5-92.3%). 37Hemagen had the lowest sensitivity (88.0-92.0%), but high specificity (99.0-100.0%). Sensitivity 38 was intermediate for Ortho (92.4-96.5%) and Wiener (94.0-97.1%); both had high specificity 39 (98.8-100.0% and 96.7-99.3%, respectively). Antibody reactivity and clinical sensitivity was 40 lowest in donors from Mexico, intermediate in those from Central America and highest in those 41 from South America. 42 43 Conclusions: Our findings provide an initial evidence base to improve laboratory diagnosis of 44 Chagas disease in the US. The best current testing algorithm would employ a high sensitivity45screening test followed by a high specificity confirmatory test.

Test performance evaluation of SARS-CoV-2 serological assays

“…Each cartridge was assigned a semi-quantitative score (0 for negative, 1 to 6 for positive) for test line intensity by two independent readers blinded to specimen status and to each other’s scores (eFigure 1). 17 For some cartridges (DeepBlue, UCP, Bioperfectus), the positive control indicator failed to appear after addition of diluent in a significant fraction of tests. For these tests, two further drops of diluent were added to successfully recover control indicators in all affected tests.…”

“…For specificity, we included 108 pre-COVID-19 plasma specimens from eligible blood donors collected prior to July 2018. 17 We assessed cross-reactivity using 52 specimens from 2020: 50 with test results for other respiratory viruses (Biofire FilmArray; BioFire Diagnostics, Salt Lake City, UT), and 32 with negative results by SARS-CoV-2 RT-PCR. We based minimum sample size calculations on expected binomial exact 95% confidence limits.…”

Antibody epitope repertoire analysis enables rapid antigen discovery and multiplex serology

“…Using Chagas disease seropositive specimens, a panel of 31 peptide motifs was identified that exhibited 100% sensitivity (60/60) and 100% specificity (120/120) in independent validation sets. Remarkably, the Chagas SERA assay exhibited 99.8% specificity (998/1000) amongst sera without known Chagas serostatus, which compares favorably to the combined sensitivity and specificity of individual, FDA-cleared tests 17 . The exceptional specificity of SERA could be expected to yield fewer false positive tests, a feature that may be useful in screening and surveillance studies 21 , particularly when multiple tests are performed in parallel.…”

“…Confirmatory testing currently requires the use of three serology tests -two parallel, independent tests, and a third "tie-breaker" test to achieve a specificity of >99%. Thus, a single test with high specificity could streamline confirmatory testing and screening in blood donors and at-risk groups 17 . Our results indicate that NGS-based serology using SERA provides an effective approach to antigen and epitope discovery, and an assay format capable of achieving exceptional diagnostic specificity without multiplexing limitations.…”

Access to Chagas disease treatment in the United States after the regulatory approval of benznidazole

“…We recognize that access to CD diagnosis is also problematic in the US [10]. While this topic was not within the scope of this study, creating access to benznidazole will require actions in relation to diagnosis, such as assessment of the four FDA-cleared diagnostic assays [18,33], development of strategies for maternal and newborn screening, education of primary care providers on diagnostic testing, and improvement of linkage to care for seropositive blood donors. Likewise, we did not consider access to nifurtimox, which is still provided by CDC for compassionate use.…”