Hidden perils: diagnosing asymptomatic disease carriers. (Special Issue: Medical testing, diagnosis and value.)

COVID-19, a disease induced by SARS-CoV-2, became a worldwide pandemic while SARS, a disease induced by a closely related virus, SARS-CoV, was successfully contained. This is because COVID-19, unlike SARS, can be spread by people who do not display any symptoms of disease, either because they are in the early stages of the infection or because their infection remains clinically silent. This research article traces the complex history of the diagnosis of symptom-free (or asymptomatic) carriers of pathogens, a term inseparably linked to the rise of the laboratory diagnosis of pathogens. Only such a diagnosis can reveal that an apparently healthy individual harbours dangerous bacteria, parasites, or viruses. The article begins with the iconic story of 'Typhoid Mary', a New York cook found to be an asymptomatic carrier of typhoid fever microbes. It then discusses divergent approaches to the treatment of symptom-free carriers of hookworm and controversies around the screening of HIV carriers, especially before the development of anti-retroviral treatments. It concludes with a presentation of the debates on the role of asymptomatic carriers in the spread of COVID-19 and of the differences between the approaches of countries seeking to eliminate this disease, a goal that itself entails tracing and isolation of all asymptomatic carriers of coronavirus, and those trying to contain it, an approach that tolerates the presence of a limited number of 'invisible' virus carriers.

'Test, test, test!': scarcity, tinkering, and testing policy early in the COVID-19 epidemic in France. (Special Issue: Medical testing, diagnosis and value.)

This article follows the introduction of COVID-19 polymerase chain reaction (PCR) diagnostic tests in France. It shows how, at the intersection of science, medicine, politics, and policy-making, the test, trace, and isolate (TTI) strategy played out during the first months of the pandemic against a backcloth of multiple shortages. In so doing, the authors move beyond trite explanations (such as 'French public health's backwardness') to highlight how successive policy inflections affected the national response to the pandemic. The piece analyses the shifting French political discourse surrounding (scarce) COVID-19 tests while exploring ad-hoc regulations and guidelines as well as the intense 'bricolage' that they triggered in the field of clinical medicine. The authors contend that the limitations of the testing infrastructure in France during the first half of 2020 shaped the decision to resort to lockdown. The research article sheds light on two coexisting registers of professional uses of reverse transcription-polymerase chain reaction (RT-PCR) assays-a 'public health use' and a 'clinical use'-and highlights the changing political and social relevance of these two registers, with scarcity as a major determinant of these changes. One of the striking aspects of the introduction of COVID-19 tests in France therefore lies in the enduring gap between the dynamics of the epidemic and the dynamics of testing. In this respect, the French situation is neither extreme nor unique, which makes this case study a relevant basis for the international comparison of testing practices in different phases of the COVID-19 pandemic.