Journal of the Royal Society of Medicine | 2021
When is a screening test not a screening test?
Abstract
The COVID-19 pandemic of 2019-2020 took governments around the world by surprise, not least that in the UK. Nevertheless, and despite all the failings of political and practical public health action of the early months, the international academic community and industry, particularly bio pharma and med-tech, were galvanised into action. The manifestations of this have been found not only in the remarkable success of the programmes to develop vaccines against COVID-19 but also in the speedy development of reverse transcription polymerase chain reaction (PCR) and rapid lateral flow device (LFD) tests for SARS-CoV-2 nuclei acid fragments and antigen, respectively. However the deployment of these tests has proved highly controversial, with public health academics in particular falling out over the appropriateness of the use of LFD for mass asymptomatic population testing, the controversy having been brought about by a government-sponsored initiative in Liverpool in November 2020, branded as SMART (Systematic Meaningful Asymptomatic Repeated Testing). The Liverpool pilot included a comparison of LFD versus PCR testing in 5869 asymptomatic adults between 6 and 29 November 2020. Excluding void results, the LFD testing showed a sensitivity relative to PCR of 40.0% and a specificity of 99.9%. This would be a direct comparison as a clinical test but is not as a public health test for infectious individuals, as PCR remains positive in the postinfectious period, often for weeks. However, popular misinterpretation of these statistics as a clinical comparison with a ‘gold standard’ led to vehement criticism of the Liverpool trial, while the Liverpool team has continued to defend the approach as a valuable tool in the fight against the COVID. Critics of LFD for mass asymptomatic population testing held the so-called gold standard criteria for evaluating screening programmes first enunciated by Wilson and Jungner in 1968. The starting point for Wilson and Jungner’s contribution in the post-war technological age and the beckoning frontiers of genetics was the growing momentum to adopting screening approaches to a widening agenda of noncommunicable conditions. The central idea of early disease detection and treatment was seen to be bringing to treatment those with previously undetected disease while avoiding harm to those not in need of treatment. The 10 classic Wilson and Jungner screening criteria for assessing the utility of a screening test encompassed the significance of the disease as a health problem; the acceptability and availability of effective treatment that was cost effective; the availability of a suitable test that was acceptable to the public and capable of recognising disease at a latent or early symptomatic stage with the natural history and progression of undiagnosed disease being well understood; that there should be an agreed policy on whom to treat as patients; and that case-finding should be a continuing process rather than a once-and-for-all project. At the time of Wilson and Jungner’s publication, infectious disease, outbreak control and the prospects of a novel pandemic had all but disappeared from the public health radar. Since 1968, efforts have been made to revisit the screening criteria they espoused, and it seems unlikely that they expected their offering to be set in stone for eternity. In particular, it has been argued that