Misuse of SARS-CoV-2 testing in symptomatic health-care staff in the UK - Authors' reply.

We thank Bernard Freudenthal for his response to our previous Correspondence. We agree that use of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) testing among health-care workers (HCWs) solely to reduce absenteeism is inappropriate. Freudenthal correctly outlines the risks, posed by false-negative results, of advising potentially infectious HCWs to return to work. Moreover, staffing levels are currently far less problematic within UK health-care settings than during the peak of the pandemic.

HCW testing should aim to identify infectious cases and reduce nosocomial transmission of SARS-CoV-2: testing only self-reported symptomatic cases risks missing many infectious cases. For instance, HCWs might unwittingly attend work with mild or non-specific symptoms. Furthermore, although the relationship between RT-PCR cycle threshold (Ct) values and infectivity requires further elucidation, evidence suggests that Ct values among asymptomatic and symptomatic cases are similar. Crucially, viable virus has been isolated up to 6 days before symptom onset.

Robust epidemiological studies help detail asymptomatic spread. Results have been heterogeneous; assumptions vary between studies which might be subject to recall bias, definitions of symptoms are inconsistent, and some studies do not account for the critical pre-symptomatic phase of infection. Nonetheless, most such studies find evidence of asymptomatic SARS-CoV-2 transmission.

False-positive results can also limit HCW screening utility. They can be biological, with dead virus detected in non-infectious cases, and technical, where a test is positive in the absence of viral RNA. Regular screening risks identification of biological false positives; however, more research is required to understand the biology of persistent viral RNA shedding. Technical false positives might be reduced to manageable levels by testing in duplicate.

We believe a symptom-agnostic testing approach for SARS-CoV-2 among HCWs is an effective measure of reducing viral transmission. This approach is advocated on a population level and might be particularly beneficial among HCWs given reports of hospitals acting as hotbeds of COVID-19.

Arguments against mass testing approaches previously have suggested a lack of resources might make this ineffective. However, UK daily testing capacity has increased tenfold since the publication of our Correspondence, while rapid point-of-care antigen tests facilitate early intervention to limit transmission.

Screening for SARS-CoV-2 in asymptomatic HCWs could be a vital weapon in the fight against COVID-19 now and over the winter months. This will help the National Health Service to maintain the capacity to treat other diseases in the face of a second wave. We must act to prevent further virus spread, economic disruption, and unnecessary death.