Diagnostic performance of LumiraDx SARS-CoV-2 rapid antigen test compared to PCR for diagnosis of COVID-19 in Liberia

BackgroundDiagnosis of SARS-CoV-2 infection in Liberia has primarily relied on polymerase chain reaction (PCR)-based testing at the countrys National Reference Laboratory. This centralized approach caused reporting delays, prompting evaluation of point-of-care antigen-based tests. We assessed the test performance of the LumiraDx SARS-CoV-2 Ag test (LumiraDx, London, UK) in this setting. MethodsWe tested ambulatory individuals screened for enrollment into an observational cohort study of COVID-19 sequelae in Monrovia in 2021. We compared the results of LumiraDx testing of anterior nasal swab specimens to the results of PCR BioFire(R) R2.1P (bioMerieux, Salt Lake City, Utah) on eluent from nasopharyngeal swabs. ResultsWe evaluated 348 individuals. Among the 274 persons with symptoms, 49.3% were PCR-positive and 36.5% were antigen-positive. The sensitivity, specificity, negative predictive value (NPV), and positive predictive value (PPV) of LumiraDx in this group were 72.6% (95% CI: 64.3%-79.9%), 98.6% (95% CI: 94.9%-99.8%), 78.7% (CI: 71.9%-84.6%), and 98.0% (CI: 93.0%-99.8%), respectively. Among the 74 asymptomatic individuals, 12.2% were positive by PCR, and 5.5% by antigen testing, resulting in a sensitivity, specificity, NPV, and PPV of LumiraDx of 44.4% (95% CI: 13.7%-78.8%), 100% (95% CI: 94.5%-100%), 92.9% (CI: 84.1%-97.6%), and 100% (CI: 39.8%-100%), respectively. ConclusionAlthough the specificity and PPV of LumiraDx for diagnosing SARS-CoV-2 were high among persons with and without symptoms, the sensitivity was unacceptably low in both groups, and much less than that reported by the manufacturer. Before new point-of-care diagnostics are adopted, test performance needs to be assessed in the local setting.