Table 1.

Analytical performances of the SIENNA™ COVID-19 SARS-CoV-2 Antigen Rapid Test Cassette (Nasopharyngeal Swab) rapid diagnostic test for the qualitative detection of the N protein of SARS-CoV-2 using 100 positive and 50 negative nasopharyngeal swab samples by reference rRT-PCRⁱ, according to their N gene C_t values.

				SIENNA™ COVID-19 Antigen Rapid Test Cassettea
		N gene Ct by rRT-PCR (median; range)	N	TP (n)	FN (n)	Sensitivityb(% [95% CI])g	Specificityb(% [95% CI])	Agreementc	Concordanced	Youden’s J indexe	PPVf(% [95% CI])	NPVf(% [95% CI])
N gene Cth of positive samples by reference rRT-PCRi	≤20	19 (9-20)	25	25	0	100.0 [99.9–100.0]	100.0 [99.9–100.0]	100.0	1.0	1.0	100.0 [99.9–100.0]	100.0 [99.9–100.0]
	21–33	25 (21–33)	52	49	3	94.2 [87.9–100.0]	100.0 [99.9–100.0]	97.0	0.94	0.94	100.0 [99.9–100.0]	98.9 [96.1–100.0]
	>33	35 (34–37)	23	16	7	69.6 [50.7–88.0]	100.0 [99.9–100.0]	90.4	0.76	0.70	92.1 [86.0 –95.7]	94.4 [88.5–100.0]
	All Ct values	24 (9–37)	100	90	10	90.0 [84.1–95.9]	100.0 [99.9–100.0]	93.3	0.86	0.90	100.0 [99.9–100.0]	98.1 [94.6–100.0]

C_t: cycle threshold; FN: false negative; FP: false positive; NPV: negative predictive value; PPV: positive predictive value; rRT-PCR: real-time reverse transcription-polymerase chain reaction; TP: true positive; TN: true negative.

^aNasopharyngeal samples were collected with a flocked swab, then discarded in 1 ml of physiological saline, and further stored frozen at −80 °C before reuse;

^bAll 50 swab samples negative by reference rRT-PCR were found negative by the test SIENNA™ COVID-19 Antigen Rapid Test Cassette (Nasopharyngeal Swab); the values of TN and FN were 50 and 0, respectively;

^cAgreement = TP + TN/TP + FP + TN + FN, expressed in percentage;

^dThe Cohen’s k coefficient calculation was used to estimate the concordance (Cohen, 1960) and interpreted according the Landis and Koch scale (Landlis and Koch, 1977), as follows: <0 as indicating no agreement, 0–0.20 as slight, 0.21–0.40 as fair, 0.41–0.60 as moderate, 0.61–0.80 as substantial, and 0.81–1 as almost perfect concordance;

^eThe accuracy of the test SIENNA™ COVID-19 Antigen Rapid Test Cassette (Nasopharyngeal Swab) to correctly diagnose SARS-CoV-2 infection was estimated by Youden’s J index (J = sensitivity + specificity − 1) (Youden, 1950);

^fPPV and NPV were calculated according to the Bayes’s formulae, by taking into account the official reported prevalence of SARS-CoV-2-RNA positivity in COVID-19-suspected patients in Paris’s area, France, of 16.2% on 17th November 2020 [Santé publique France, 2020; https://www.santepubliquefrance.fr/];

^g95% confidence intervals in brackets were calculated by using the Wilson score bounds;

^hThe Ct values of N gene detection by the reference Seegene rRT-PCR were used to classify nasopharyngeal samples according to their level of SARS-CoV-2 RNA excretion; C_t of 20 and 33 were taken as thresholds of very high and high SARS-CoV-2 RNA excretion, respectively, as previously stated (Centers for Disease Control and Prevention, 2020b; Jefferson et al., 2020; Société Française de Microbiologie, 2020; Yu et al., 2020);

ⁱThe CE IVD-marked Allplex™ 2019-nCoV Assay (Seegene, Séoul, Korée) constituted the reference multiplex rRT-PCR for SARS-CoV-2 RNA detection. This assay detects three target genes of SARS-CoV-2 (E, RdRP and N genes) (Farfour et al., 2020).