Table 2.
Antigen and PCR test result concordance for each type of sample.
| (A) Antigen test (reagent) vs RT-qPCR (VTM) | |||
|---|---|---|---|
| All | RT-qPCR |
||
| Positive | Negative | Total | |
| Antigen + | 6 | 4 | 10 |
| Antigen – | 11 | 14 | 25 |
| Positive concordance rate, % (95% CI) | 35 (13–58) | ||
| Negative concordance rate, % (95% CI) | 78 (59–97) | ||
| Cohen’s kappa (standard error) | 0.13 (0.15) | ||
| Gwet’s AC1 statics (standard error) | 0.19 (0.18) | ||
| Appropriate timing | RT-qPCR | ||
| (Between 2 and 9 days from symptom onset) | |||
| Positive | Negative | Total | |
| Antigen + | 4 | 2 | 6 |
| Antigen – | 3 | 0 | 3 |
| Positive concordance rate, % (95% CI) | 57 (20–94) | ||
| Negative concordance rate, % (95% CI) | 0 (0–59) | ||
| Cohen’s kappa (standard error) | −0.36 (0.17) | ||
| Gwet’s AC1 statics (standard error) | 0.072 (0.39) | ||
| Not appropriate timing | RT-qPCR | ||
| (>9 days from symptom onset) | |||
| Positive | Negative | Total | |
| Antigen + | 2 | 2 | 4 |
| Antigen – | 8 | 14 | 22 |
| Positive concordance rate, % (95% CI) | 20 (0.0–45) | ||
| Negative concordance rate, % (95% CI) | 88 (71–100) | ||
| Cohen’s kappa (standard error) | 0.085 (0.17) | ||
| Gwet’s AC1 statics (standard error) | 0.37 (0.20) | ||
| (B) Antigen test (reagent) vs RT-qPCR (reagent) | |||
|---|---|---|---|
| All | RT-qPCR |
||
| Positive | Negative | Total | |
| Antigen + | 13 | 2 | 15 |
| Antigen – | 19 | 6 | 25 |
| Positive concordance rate, % (95% CI) | 41 (24–58) | ||
| Negative concordance rate, % (95% CI) | 75 (45–100) | ||
| Cohen’s kappa (standard error) | 0.087 (0.10) | ||
| Gwet’s AC1 statics (standard error) | −0.019 (0.17) | ||
| Appropriate timing | RT-qPCR | ||
| (Between 2 and 9 days from symptom onset) | |||
| Positive | Negative | Total | |
| Antigen + | 9 | 1 | 10 |
| Antigen – | 1 | 2 | 3 |
| Positive concordance rate, % (95% CI) | 90 (71–100) | ||
| Negative concordance rate, % (95% CI) | 67 (13–100) | ||
| Cohen’s kappa (standard error) | 0.57 (0.27) | ||
| Gwet’s AC1 statics (standard error) | 0.76 (0.17) | ||
| Not appropriate timing | RT-qPCR | ||
| (>9 days from symptom onset) | |||
| Positive | Negative | Total | |
| Antigen + | 4 | 1 | 5 |
| Antigen – | 18 | 4 | 22 |
| Positive concordance rate, % (95% CI) | 18 (2.1–34) | ||
| Negative concordance rate, % (95% CI) | 80 (45–100) | ||
| Cohen’s kappa (standard error) | −0.0079 (0.085) | ||
| Gwet’s AC1 statics (standard error) | −0.40 (0.18) | ||
| (C) Antigen test (VTM) vs RT-qPCR (VTM) | |||
|---|---|---|---|
| All | RT-qPCR |
||
| Positive | Negative | Total | |
| Antigen + | 52 | 1a | 53 |
| Antigen – | 76 | 100 | 176 |
| Positive concordance rate, % (95% CI) | 41 (32–49) | ||
| Negative concordance rate, % (95% CI) | 99 (97–100) | ||
| Cohen’s kappa (standard error) | 0.37 (0.046) | ||
| Gwet’s AC1 statics (standard error) | 0.36 (0.064) | ||
| Appropriate timing | RT-qPCR | ||
| (Between 2 and 9 days from symptom onset) | |||
| Positive | Negative | Total | |
| Antigen + | 34 | 0 | 34 |
| Antigen – | 13 | 11 | 24 |
| Positive concordance rate, % (95% CI) | 72 (60–85) | ||
| Negative concordance rate, % (95% CI) | 100 (100–100) | ||
| Cohen’s kappa (standard error) | 0.50 (0.11) | ||
| Gwet’s AC1 statics (standard error) | 0.61 (0.11) | ||
| Not appropriate timing | RT-qPCR | ||
| (>9 days from symptom onset) | |||
| Positive | Negative | Total | |
| Antigen + | 18 | 1 | 19 |
| Antigen – | 63 | 89 | 152 |
| Positive concordance rate, % (95% CI) | 22 (13–31) | ||
| Negative concordance rate, % (95% CI) | 99 (97–100) | ||
| Cohen’s kappa (standard error) | 0.22 (0.051) | ||
| Gwet’s AC1 statics (standard error) | 0.36 (0.077) | ||
RT-qPCR, reverse transcription quantitative polymerase chain reaction; VTM, viral transport medium; CI, confidence interval.
a
RT-qPCR was positive by another RT-qPCR kit (SARS-CoV-2 Direct Detection RT-qPCR Kit, Takara Bio).