Virus variant-specific clinical performance of SARS coronavirus two rapid antigen tests in point-of-care use, from November 2020 to January 2022

Abstract

Objectives: Antigen rapid diagnostic tests (RDTs) for SARS coronavirus 2 (SARS-CoV-2) are quick, widely available, and inexpensive. Consequently, RDTs have been established as an alternative and additional diagnostic strategy to quantitative reverse transcription polymerase chain reaction (RT-qPCR). However, reliable clinical and large-scale performance data specific to a SARS-CoV-2 virus variant of concern (VOC) are limited, especially for the Omicron VOC. The aim of this study was to compare RDT performance among different VOCs.

Methods: This single-centre prospective performance assessment compared RDTs from three manufacturers (NADAL, Panbio, MEDsan) with RT-qPCR including deduced standardized viral load from oropharyngeal swabs for detection of SARS-CoV-2 in a clinical point-of-care setting from November 2020 to January 2022.

Results: Among 35 479 RDT/RT-qPCR tandems taken from 26 940 individuals, 164 of the 426 SARS-CoV-2 positive samples tested true positive with an RDT corresponding to an RDT sensitivity of 38.50% (95% CI, 34.00-43.20%), with an overall specificity of 99.67% (95% CI, 99.60-99.72%). RDT sensitivity depended on viral load, with decreasing sensitivity accompanied by descending viral load. VOC-dependent sensitivity assessment showed a sensitivity of 42.86% (95% CI, 32.82-53.52%) for the wild-type SARS-CoV-2, 43.42% (95% CI, 32.86-54.61%) for the Alpha VOC, 37.67% (95% CI, 30.22-45.75%) for the Delta VOC, and 33.67% (95% CI, 25.09-43.49%) for the Omicron VOC. Sensitivity in samples with high viral loads of ≥10⁶ SARS-CoV-2 RNA copies per mL was significantly lower in the Omicron VOC (50.00%; 95% CI, 36.12-63.88%) than in the wild-type SARS-CoV-2 (79.31%; 95% CI, 61.61-90.15%; p 0.015).

Discussion: RDT sensitivity for detection of the Omicron VOC is reduced in individuals infected with a high viral load, which curtails the effectiveness of RDTs. This aspect furthert: limits the use of RDTs, although RDTs are still an irreplaceable diagnostic tool for rapid, economic point-of-care and extensive SARS-CoV-2 screening.

Keywords: Antigen rapid diagnostic test; Clinical performance evaluation; Omicron; PCR; SARS-CoV-2; Virus variants of concern.

Graphical abstract

Fig. 1

Distribution of enrolled rapid diagnostic test (RDT) results. Four hundred sixty-nine cases of multiple RDT performances per day per person and 20 cases of recent deisolation after SARS coronavirus 2 (SAR-CoV-2) infection were excluded from data analysis. Twenty-six RDTs with invalid test results (missing positive control or interfering lines, 5 NADAL, 11 Panbio, and 10 MEDsan) were also not taken into account. RT-qPCR, quantitative reverse transcription polymerase chain reaction.

Fig. 2

Sensitivity of antigen rapid diagnostic testing (RDT) compared with that of quantitative reverse transcription polymerase chain reaction by manufacturer and viral load (a) Sensitivity and (b) specificity of antigen rapid diagnostic tests from three manufacturers (nal von minden NADAL, Abbott Panbio, and MEDsan) compared with those of quantitative reverse transcription polymerase chain reaction (RT-qPCR) as reference standard (n = 35 479). (c) Viral load of an RT-qPCR–positive specimen that tested positive and negative by RDTs. (d) Sensitivity of RDT compared with that of RT-qPCR in relation to viral load determined from C_t values. Sensitivity is sharply increasing with higher viral loads (n = 426). The dotted lines in (c) and (d) represent the viral load of 10⁶ SARS coronavirus 2 (SARS-CoV-2) RNA copies per mL, assumed as infectivity threshold [14]. The asterisks represent a p value of <0.0001.

Fig. 3

Variant of concern (VOC) depending on antigen rapid diagnostic test (RDT) sensitivity. Antigen rapid diagnostic test sensitivity compared with that of quantitative reverse transcription polymerase chain reaction as reference standard by VOC. (a) Included 257 samples with molecularly confirmed VOC. (b) Included 407 samples with either molecularly confirmed VOC or epidemiologically assigned VOC (in case no VOC was determined molecularly and the VOC of the infection source was known or a VOC was responsible for more than 90% of all coronavirus disease 2019 cases in Germany at the time of sampling). (c) Included 218 samples with a viral load of <10⁶ SARS coronavirus 2 (SARS-CoV-2) RNA copies per mL and an either molecularly or epidemiologically assigned wild-type, Alpha VOC, Delta VOC, or Omicron VOC. (d) Included 184 samples with a viral load of ≥10⁶ SARS-CoV-2 RNA copies per mL and an either molecularly or epidemiologically assigned wild-type SARS-CoV-2, Alpha VOC, Delta VOC, or Omicron VOC. The asterisk represents a p value of <0.05.

Fig. 4

Variant of concern (VOC) depending level of detection (LOD), overall and by manufacturer. Included 402 samples either molecularly confirmed or epidemiologically assigned to wild-type virus, Alpha VOC, Delta VOC, or Omicron VOC (in case no VOC was determined molecularly and the VOC of the infection source was known or a VOC was responsible for more than 90% of all coronavirus disease 2019 cases in Germany at the time of sampling). Further, 50% and 95% LODs were marked by dashed vertical lines with 95% CIs visualized in grey (50% LOD) and yellow (95%), respectively. The regression curve is shown as a straight line with 95% CI visualized in blue. The difference in overall 50% LOD was significantly higher for Omicron VOC than for wild-type virus, whereas a nonsignificant increase in 50% and 95% LOD was observed from wild-type virus over Alpha VOC, Delta VOC in the overall data, and for Abbott Panbio (n = 156) and MEDsan (n = 197). Owing to the limited case numbers, no reliable VOC-specific LOD calculation could be obtained for nal von minden NADAL (n = 49).