Table 4.
Multivariable binomial logistic regression model for a positive SARS-CoV-2 PCR result among patients meeting a clinical and radiological reference standard for COVID-19a
| Model 1 | Model 2 | |||
|---|---|---|---|---|
| Characteristic | Odds ratio (95% CI) | P value | Odds ratio (95% CI) | P value |
| Age, per year | 1.00 (0.99 – 1.02) | 0.54 | 1.00 (0.99 – 1.02) | 0.59 |
| Duration of symptoms at time of PCR testingb | 0.21 | 0.20 | ||
| 3 days | Reference | Reference | ||
| 5 days | 1.09 (0.89 – 1.35) | 1.14 (0.92 – 1.41) | ||
| 7 days | 1.13 (0.88 – 1.45) | 1.22 (0.93 – 1.62) | ||
| 9 days | 1.08 (0.46 – 2.55) | 1.25 (0.86 – 1.80) | ||
| 14 days | 0.76 (0.01 – 56.8) | 1.14 (0.63 – 2.06) | ||
| Number of comorbidities, per additional comorbidity | 1.22 (1.04 – 1.43) | 0.02 | ||
| Current, vs never or ex-smoker | 0.23 (0.12 – 0.42) | <0.001 | 0.25 (0.13 – 0.50) | <0.001 |
| Received oxygen therapy | 1.90 (1.10 – 3.27) | 0.02 | 1.89 (1.09 – 3.29) | 0.02 |
| COPD | 0.95 (0.48 – 1.88) | 0.89 | ||
| Other respiratory disease | 0.77 (0.27 – 2.17) | 0.62 | ||
| Chronic heart disease | 2.87 (1.51 – 5.44) | 0.001 | ||
a
Model 1 adjusted for age, duration of symptoms, number of comorbidities, smoking and receipt of oxygen therapy (as a marker of disease severity). Model 2 adjusted for additional confounders associated with smoking comprising COPD, chronic heart disease and respiratory disease. b A cubic spline for duration of symptoms at time of testing with four knots was included in the model. P value presented for this variable is the Wald likelihood test comparing a model including the cubic spline variable with one without it.