RESUMO
OBJECTIVES: Compared to RT-PCR, lower performance of antigen detection assays, including the Lumipulse G SARS-CoV-2 Ag assay, may depend on specific testing scenarios. METHODS: We tested 594 nasopharyngeal swab samples from individuals with COVID-19 (RT-PCR cycle threshold [Ct] values ≤ 40) or non-COVID-19 (Ct values >40) diagnoses. RT-PCR positive samples were assigned to diagnostic, screening, or monitoring groups of testing. RESULTS: With a limit of detection of 1.2 × 104 SARS-CoV-2 RNA copies/mL, Lumipulse showed positive percent agreement (PPA) of 79.9% (155/194) and negative percent agreement of 99.3% (397/400), whereas PPAs were 100% for samples with Ct values of <18 or 18-<25 and 92.5% for samples with Ct values of 25-<30. By three groups, Lumipulse showed PPA of 87.0% (60/69), 81.1% (43/53), or 72.2% (52/72), respectively, whereas PPA was 100% for samples with Ct values of <18 or 18-<25, and was 94.4, 80.0, or 100% for samples with Ct values of 25-<30, respectively. Additional testing of RT-PCR positive samples for SARS-CoV-2 subgenomic RNA showed that, by three groups, PPA was 63.8% (44/69), 62.3% (33/53), or 33.3% (24/72), respectively. PPAs dropped to 55.6, 20.0, or 41.7% for samples with Ct values of 25-<30, respectively. All 101 samples with a subgenomic RNA positive result had a Lumipulse assay's antigen positive result, whereas only 54 (58.1%) of remaining 93 samples had a Lumipulse assay's antigen positive result. CONCLUSIONS: Lumipulse assay was highly sensitive in samples with low RT-PCR Ct values, implying repeated testing to reduce consequences of false-negative results.
Assuntos
COVID-19/diagnóstico , RNA Viral/análise , Reação em Cadeia da Polimerase Via Transcriptase Reversa/métodos , SARS-CoV-2/genética , COVID-19/virologia , Teste de Ácido Nucleico para COVID-19 , Humanos , Limite de Detecção , Nasofaringe/virologia , Kit de Reagentes para Diagnóstico , SARS-CoV-2/isolamento & purificação , Sensibilidade e EspecificidadeRESUMO
A diagnostic algorithm for SARS-CoV-2 infection in patients admitted to the emergency area, based on a combination of rapid antigen and molecular testing, has been evaluated with 3070 nasopharyngeal swabs. Compared to molecular test alone, the proposed algorithm allowed to significantly reduce costs and average time to results.