Table 3.
Linear regression analyses for the RT-qPCR Ct value across the different categories of infections, adjusting for sex, age, nationality, reason for RT-qPCR testing, and calendar week of RT-qPCR testa.
| Original sample size | RT-qPCR Ct value | Univariable regression analysis | Multivariable regression analysis | ||||
|---|---|---|---|---|---|---|---|
| N (%) | Mean (SD) | p value | β (95% CI) | p value | Adjusted β (95% CI) | p value | |
| Study group | |||||||
| Primary infections in unvaccinated individuals | 301,424 (98.0) | 24.4 (6.3) | <0.001 | Reference | Reference | ||
| Reinfections in unvaccinated individuals | 1695 (0.6) | 28.0 (6.4) | 3.61 (3.30–3.91) | <0.001 | 3.67 (3.38–3.96) | <0.001 | |
| BNT162b2-vaccine breakthrough infections | 4262 (1.4) | 24.9 (6.5) | 0.60 (0.40–0.79) | <0.001 | 0.82 (0.63–1.01) | <0.001 | |
| mRNA-1273-vaccine breakthrough infections | 283 (0.1) | 30.2 (6.0) | 5.82 (5.08–6.56) | <0.001 | 3.29 (2.58–4.00) | <0.001 | |
| Sex | |||||||
| Male | 220,318 (71.6) | 24.6 (6.4) | <0.001 | Reference | Reference | ||
| Female | 87,346 (28.4) | 23.9 (6.2) | −0.61 (−0.66 to −0.56) | <0.001 | −0.45 (−0.50 to −0.40) | <0.001 | |
| Age group | |||||||
| 20–29 yearsb | 67,040 (21.8) | 24.7 (6.5) | <0.001 | Reference | Reference | ||
| <10 years | 21,981 (7.1) | 26.4 (5.7) | 1.72 (1.63–1.82) | <0.001 | 2.13 (2.04–2.23) | <0.001 | |
| 10–19 years | 23,581 (7.7) | 23.9 (6.0) | −0.80 (-0.90 to −0.71) | <0.001 | −0.29 (−0.38 to −0.20) | <0.001 | |
| 30–39 years | 106,493 (34.6) | 24.3 (6.5) | −0.39 (−0.45 to −0.33) | <0.001 | −0.20 (−0.26 to −0.15) | <0.001 | |
| 40–49 years | 58,072 (18.9) | 24.1 (6.3) | −0.60 (−0.67 to −0.53) | <0.001 | −0.28 (−0.34 to −0.21) | <0.001 | |
| 50–59 years | 22,299 (7.2) | 23.9 (6.2) | −0.78 (−0.87 to −0.68) | <0.001 | −0.41 (−0.50 to −0.32) | <0.001 | |
| 60–69 years | 6360 (2.1) | 23.5 (6.1) | −1.15 (−1.31 to −0.98) | <0.001 | −0.82 (−0.97 to −0.66) | <0.001 | |
| 70+ years | 1838 (0.6) | 23.3 (6.0) | −1.38 (−1.67 to −1.09) | <0.001 | −1.04 (−1.32 to −0.76) | <0.001 | |
| Reason for RT-qPCR testing | |||||||
| Clinical suspicion | 110,948 (36.1) | 23.1 (6.0) | <0.001 | Reference | Reference | ||
| Pre-travel | 4557 (1.5) | 26.3 (6.4) | 3.26 (3.08–3.44) | <0.001 | 3.64 (3.46–3.82) | <0.001 | |
| Port of entry | 33,287 (10.8) | 26.6 (6.7) | 3.56 (3.49–3.64) | <0.001 | 3.55 (3.46–3.63) | <0.001 | |
| Survey | 48,361 (15.7) | 25.6 (6.3) | 2.56 (2.50–2.63) | <0.001 | 2.76 (2.69–2.82) | <0.001 | |
| Individual request | 15,489 (5.0) | 24.7 (6.4) | 1.66 (1.55–1.76) | <0.001 | 2.22 (2.11–2.32) | <0.001 | |
| Contact tracing | 67,159 (21.8) | 25.1 (6.1) | 2.04 (1.98–2.10) | <0.001 | 1.70 (1.64–1.76) | <0.001 | |
| Healthcare routine testing | 21,014 (6.8) | 21.5 (6.2) | −1.60 (−1.69 to −1.51) | <0.001 | −0.84 (−0.94 to −0.75) | <0.001 | |
| Other | 6849 (2.2) | 25.3 (6.4) | 2.21 (2.06–2.36) | <0.001 | 1.87 (1.71–2.02) | <0.001 | |
CI confidence interval, Ct cycle threshold, RT-qPCR real-time reverse transcription polymerase chain reaction, SD standard deviation.
aAnalyses were conducted on the full sample including all infections diagnosed using TaqPath COVID-19 Combo Kits platform. Categories for calendar week of RT-qPCR test are not presented in the table for brevity.
b20–29 years was chosen as a reference category because it is the first fully adult age group.