Background: Uncertainty in patients’ COVID-19 status contributes to treatment delays, nosocomial transmission, and operational pressures in hospitals. However, typical turnaround time for laboratory PCR remains 12-24h and lateral flow testing (LFD) has limited sensitivity. We recently demonstrated that AI-driven triage (CURIAL-1.0) provides rapid COVID-19 screening using clinical data routinely available within 1h of arrival to hospital. Here we aimed to improve time-to-result, perform external & prospective validation, and deploy a novel lab-free screening tool in a UK emergency department. Methods: We eliminated weakly-informative predictors to improve generalisability and speed, developing CURIAL-Lab with vital signs and readily available blood tests (FBC, U&E, LFT, CRP) and CURIAL-Rapide with vital signs and FBC alone. Models were validated externally for emergency admissions to University Hospitals Birmingham, Bedfordshire Hospitals & Portsmouth Hospitals University NHS trusts, and prospectively at Oxford University Hospitals, by comparison to confirmatory nucleic acid testing. Next, we compared model performance with LFDs and evaluated a combined pathway triaging patients to COVID-19-suspected clinical areas where either model prediction or LFD results were positive. Lastly, we deployed CURIAL-Rapide alongside an approved point-of-care FBC analyser to provide lab-free COVID-19 screening at the John Radcliffe Hospital (Oxford, UK). Our primary improvement outcome was time-to-result. Findings: 72,223 patients met eligibility criteria across four validating hospital groups. CURIAL-Lab & CURIAL-Rapide performed consistently (AUROC range 0.858-0.881 & 0.836-0.854), achieving highest sensitivity at Portsmouth Hospitals (84.1% [Wilson’s 95% CIs 82.5-85.7] & 83.5% [81.8-85.1]) at specificities of 71.3% (70.9-71.8) and 63.6% (63.1-64.1). When combined with LFDs, models predictions improved triage sensitivity from 56.9% for LFDs alone to 85.6% with CURIAL-Lab (81.6-88.9; AUROC 0.925) and 88.2% with CURIAL-Rapide (84.4-91.1; AUROC 0.919), thereby reducing missed COVID-19 cases by 65% & 72%. In prospective deployment of CURIAL-Rapide, 520 patients were enrolled for point-of-care FBC analysis, of whom 436 received confirmatory PCR testing and 10 (2.3%) tested positive. Median time from arrival to CURIAL-Rapide result was 45:00min (32-64), 16:00min (26.3%) sooner than LFD (61:00min, 37-99; log-rank p<0.0001), and 6:52h (90.2%) sooner than PCR (7:37h, 6:05-15:39; p<0.0001). Classification performance was high, with sensitivity of 87.5% (52.9-97.8), specificity of 85.4% (81.3-88.7) and NPV 99.7% (98.2-99.9). CURIAL-Rapide correctly excluded infection for 58.5% of patients who were triaged by a physician to a ‘COVID-19-suspected’ area but went on to test negative by PCR. Impact: Our findings demonstrate the generalisability, performance and real-world operational benefits of AI driven screening for COVID-19 over standard-care in emergency departments. CURIAL-Rapide provides rapid, lab-free screening when used with near-patient FBC analysis, and can reduce the number of COVID-19- negative patients triaged to COVID-19-suspected areas.
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