149 S/F94 as a proxy for COVID-19 severity 7 with high values in survivors, and low values in non-survivors (Figure 2A). Finally, in order to make a meaningful comparison with the S/F94 at the day of enrolment, we preferred timepoints that were at least a few days after enrolment. We therefore chose day 5 as the primary timepoint for comparison. The distribution of measured S/ F94values and assigned maximum/ minimum values for those who were discharged/ died can be seen in (Figure 2B). On day 5, 1077 out of 7,312 (14.7%) known S/ N=33779 N=4989 N=10007 N=2566 N=1564 N=6235 N=1424 N=785 N=4131 N=882 N=523 N=464 N=411 1 2 3 4 5 0 1 2 3 4 5 6 7 8 9 10 11 12 Day S/F94 28−day outcome Discharged alive Death S/F94 in the first 12 days since admission 0 200 400 600 800 1 2 3 4 S/F94 day 5 Count Measured Assigned max/min if discharged/died N=40842 0.0 0.2 0.4 0.6 0.8 1 2 3 4 S/F94 day 5 Risk of 28−day mortality N=5302 1 2 3 4 4 Hosp 5 Ox 6 CPAP/HFNO 7 IMV 8 IMV S/F<2 9 MOF 10 Dead WHO ordinal severity scale S/F94 day5 N=6235 a b c d Figure 2. Evaluation of S/F94 in observational data. (a) Smoothed distributions of S/F94 values in survivors and non-survivors during the first 12 days of the study, not including assigned minimum/maximum values (restricted to 39,765 patients aged 20-75, oxygen therapy within 3 days). (b) Histogram showing distribution of S/F94 values on day 5 as used for subsequent analyses (in purple). Patients discharged home before day 5 are assigned the maximum value (4.78), and patients who died before day 5 are assigned to an arbitrary minimum of 0.5 (in black). (c) Distribution of S/F94 values day 5 compared with WHO ordinal scale2 value at the same time point, in patients who met our inclusion criteria (aged 20-75, oxygen therapy within 3 days). No assigned minimum or maximum values are included in this figure. Hosp = hospitalised, no oxygen support; Ox = Hospitalised, oxygen by mask or nasal prongs; CPAP/HFNO = Hospitalised, oxygen by continuous positive airway pressure; high-flow nasal oxygen or non-invasive ventilation; IMV = Intubation and mechanical ventilation; IMV S/F ≤ 2 = Mechanical ventilation; S/F ≤ 2 or vasopressors; MOF = Multi-organ failure & mechanical ventilation & S/F ≤ 2 & ECMO or renal replacement therapy. (d) Logistic regression analysis with 95% confidence interval, using both S/F94 on day 0 and S/F94 on day 5 as covariates, showing a clear association between mortality at 28 days and S/F94 value on day 5.
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