Use of the FebriDx point-of-care assay as part of a triage algorithm for medical admissions with possible COVID-19

ABSTRACT Background Patients admitted to hospital with COVID-19 need rapid identification and isolation to prevent nosocomial transmission. However, isolation facilities are often limited, and SARS-CoV-2 RT-PCR results are often not available when discharged from the emergency department. We evaluated a triage algorithm to isolate patients with suspected COVID-19 using simple clinical criteria and the FebriDx assay. Design Retrospective observational cohort Setting Large acute care hospital in London, UK Participants All medical admissions from the ED between 10 th August 2020 and 4 th November 2020 with valid SARS-CoV-2 RT-PCR. Interventions Medical admissions were triaged as likely, possible or unlikely COVID-19 based on clinical criteria. Patients triaged as possible COVID-19 underwent FebriDx lateral flow assay on capillary blood, and those positive for MxA were managed as likely COVID-19. Primary Outcome measures Diagnostic accuracy (sensitivity, specificity and predictive values) of the algorithm and the FebriDx assay compared to SARS-CoV-2 RT-PCR from nasopharyngeal swabs as the reference standard. Results 4.0% (136/3,443) of medical admissions had RT-PCR confirmed COVID-19. Prevalence of COVID-19 was 45.7% (80/175) in those triaged as likely, 4.1% (50/1,225) in possible and 0.3% (6/2,033) in unlikely COVID-19. Compared to SARS-CoV-2 RT-PCR, clinical triage had sensitivity of 95.6% (95%CI: 90.5% - 98.0%) and specificity of 61.5% (95%CI: 59.8% - 63.1%), whilst the triage algorithm including FebriDx had sensitivity of 92.6% (95%CI: 86.8% - 96.0%) and specificity of 86.4% (95%CI: 85.2% - 87.5%). The triage algorithm reduced the need for 2,859 patients to be admitted to isolation rooms. Ten patients missed by the algorithm had mild or asymptomatic COVID-19. Conclusions A triage algorithm including FebriDx assay had good sensitivity and was useful to ‘rule-out’ COVID-19 among medical admissions to hospital. STRENGTHS AND LIMITATIONS OF THIS STUDY Pragmatic study including a large cohort of consecutive medical admissions providing routine clinical care. A single SARS-CoV-2 RT-PCR is an imperfect reference standard for COVID-19. Multiple RT-PCR platforms used, with different PCR targets and performance. A higher prevalence of COVID-19 or other respiratory pathogens might alter performance. Criteria for likely and possible COVID-19 groups changed subtly during the study period.