Real-world evaluation of COVID-19 lateral flow device (LFD) mass-testing in healthcare workers at a London hospital; a prospective cohort analysis

Lamb, Georgia; Heskin, Joseph; Randell, Paul; Mughal, Nabeela; Moore, Luke SP; Jones, Rachael; Davies, Gary W; Rayment, Michael

Objectives: Real-world evaluation of the performance of the Innova lateral flow immunoassay antigen device (LFD) for regular COVID-19 testing of hospital workers. Methods: This prospective cohort analysis took place at a London NHS Trust. 5076 secondary care healthcare staff participated in LFD testing from 18 November 2020 - 21 January 2021. Staff members submitted results and symptoms via an online portal twice weekly. Individuals with positive LFD results were invited for confirmatory SARS CoV-2 PCR testing. The positive predictive value (PPV) of the LFD was measured. Secondary outcome measures included time from LFD result to PCR test and staff symptom profiles. Results: 284/5076 individuals reported a valid positive LFD result, and a paired PCR result was obtained in 259/284 (91•2%). 244 were PCR positive yielding a PPV of 94•21% (244/259, 95% CI 90•73% to 96•43%). 204/259 (78•8%) staff members had the PCR within 36 hours of the LFD test. Symptom profiles were confirmed for 132/244 staff members (54•1%) with positive PCR results (true positives) and 13/15 (86•6%) with negative PCR results (false positives). 91/132 true positives (68•9%) were symptomatic at the time of LFD testing: 65/91 (71•4%) had symptoms meeting the PHE case definition of COVID-19, whilst 26/91 (28•6%) had atypical symptoms. 18/41 (43•9%) staff members who were asymptomatic at the time of positive LFD developed symptoms in the subsequent four days. 9/13 (76•9%) false positives were asymptomatic, 1/13 (7•7%) had atypical symptoms and 3/13 (23•1%) had symptoms matching the PHE case definition. Conclusions: The PPV of the Innova LFD is high when used amongst hospital staff during periods of high prevalence of COVID-19, yet we find frequent use by symptomatic staff rather than as a purely asymptomatic screening tool. LFD testing does allow earlier isolation of infected workers and facilitates detection of individuals whose symptoms do not qualify for PCR testing.