Rapid Antigen and Antibody Microfluidic Immunofluorescence Assays Compared to Culture, PCR, and Laboratory Reference Tests: Performance in a Longitudinal Cohort

We evaluated the performance of rapid antigen (RAg) and antibody (RAb) microfluidic diagnostics with serial sampling of 71 participants at 6 visits over 2 months following severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. Rapid tests showed strong agreement with laboratory references (κAg = 81.0%; κAb = 87.8%). RAg showed substantial concordance to both virus growth in culture and PCR positivity 0-5 days since symptom onset (κAg-culture = 60.1% and κAg-PCR = 87.1%). PCR concordance to virus growth in culture was similar (κPCR-culture = 70.0%), although agreement between RAg and culture was better overall (κAg-culture = 45.5% vs κPCR-culture = 10.0%). Rapid antigen and antibody testing by microfluidic immunofluorescence platform are highly accurate for characterization of acute infection.

310. Longitudinal Assessment of Point-of-Care LumiraDx Antigen and Antibody Test Performance During Acute SARS-CoV-2 Infection and Recovery

Background

Rapid COVID-19 tests can offer significant advantages and reduce health disparities. The LumiraDx SARS-CoV-2 platform can perform microfluidic fluorescence assays for the rapid detection of SARS-CoV-2 antigen (Ag) and antibodies (Ab). We evaluated both tests in a longitudinal cohort to evaluate performance during acute SARS-CoV-2 infection and recovery.

Methods

We collected nasal samples from 71 unique participants at four clinic visits spanning 0-21 days since symptom onset (DSSO); blood samples were collected from the same participants over six visits spanning 0-87 DSSO. For Ag testing, 232 anterior nasal swabs were assayed by: 1) the LumiraDx Ag test, 2) a laboratory-based electrochemiluminescence immunoassay for N Ag, 3) RT-PCR (Hologic Panther Fusion), and 4) culture (growth in VeroE6AT cells). For Ab testing, 308 serum samples were assayed by: 1) the LumiraDx Ab test and 2) Roche Elecsys Anti-S SARS-CoV-2 total Ab test. Measures of concordance [positive predictive agreement (PPA), negative predictive agreement (NPA), and Cohen’s Kappa (Κ)] were estimated for qualitative results of the LumiraDx tests versus corresponding lab reference tests. Confidence intervals were estimated via bootstrapping.

Results

LumiraDx Ag results had strong agreement with lab N-Ag results (Κ > 0.80) across all samples. Between 0-5 days, agreement was perfect, except for one sample resulting positive by LumiraDx Ag and negative by lab Ag. Agreement with PCR results was moderate overall (Κ=0.60), though substantial (Κ > 0.6) for both 0-5 DSSO (PPA=0.96/NPA=0.80) and 6-10 DSSO (PPA=0.96/NPA=0.59). Agreement with culture results was moderate overall (Κ=0.46): substantial (Κ=0.6) between 0-5 DSSO (PPA=0.96/NPA=0.60) and fair (Κ=0.29) between 6-10 DSSO (PPA=1.0/NPA=0.32).

LumiraDx Ab results showed almost perfect agreement with lab Ab results across all samples (Κ=0.88), with substantial agreement (Κ > 0.7) for samples collected 0-10 DSSO (PPA=0.93/NPA=0.89) and 11-28 DSSO (PPA=0.99/NPA=0.69).

Longitudinal agreement of LumiraDx antigen test result and culture positivity, by PCR Ct value.

Nasal samples grouped by participant (lines) and agreement of results between LumiraDx antigen test result and culture positivity (proxy for infectiousness).

Conclusion

LumiraDx rapid tests perform well compared to more costly and time-consuming lab methods of Ag and Ab detection. The rapid Ag test may be helpful in identifying patients infectious between 0-5 DSSO, given the substantial concordance of the rapid Ag test and culture positivity.

Disclosures

Daphne Hamilton, BA, Roche (spouse is employed by Roche): Employee.