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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.

Abstract: Since the first recorded case of COVID-19 on February 26, 2020, Brazil has seen an exponential growth in the number of cases and deaths. The national testing approach has been insufficient to correctly use this tool in the support of containing the epidemic in the country. In this communication, we discuss efforts and challenges to scale-up COVID-19 testing at the Brazilian Unified National Health System (SUS). This communication presents the initial results of the research project created to investigate the political, industrial, technological, and regulatory aspects that may affect the diagnostic and testing capacity for COVID-19 in Brazil. The paper draws on the review of academic literature, media publication, and collection of public data on tests purchase and regulation. It enlists initiatives to enhance PCR testing, national production and development of technologies, as well as regulatory measures to fast-track new tests. Our analysis indicates some points of reflection. Firstly, the lack of a consistent national strategy to fight COVID-19 exarcebated supply problems of diagnostic components. If the country was eventually able to circumvent this situation, it still faces a more structural dependency on the importation of diagnostic components. Secondly, the discontinued funding and distribution of tests may have implied health policy fragmentation and the growing importance of local governments and non-state actors to fighting the epidemics within SUS. Finally, initiatives established since the second semester of 2020 have expanded the testing capacity at SUS. However, it has not been sufficient to control the progress of the epidemic in the country.