RESUMEN
We report colorimetric detection of SARS-CoV-2 viral RNA by an in vitro transcription/translation assay with crude E. coli extracts at room temperature, with the aid of body heat. Clinically-relevant concentrations of viral RNA (ca. 600 copies/test) were detected from synthetic RNA samples. The activation of cell-free gene expression was achieved by toehold-switch-mediated riboregulatory elements that are specific to viral RNA sequences. The colorimetric output was generated by the -complementation of {beta}-galactosidase {omega}-fragment (LacZ{omega}) with cell-free expressed LacZ, using an X-gal analogue as a substrate. The estimated cost of single reaction is <{euro}1/test, which may facilitate diagnostic kit accessibility in developing countries.
RESUMEN
Efficient wide-scale testing for SARS-CoV-2 is crucial for monitoring the incidence of the infection in the community. The gold standard for COVID-19 diagnosis is the molecular analysis of epithelial secretions from the upper respiratory system captured by nasopharyngeal (NP) swabs, which requires the intervention of trained personnel. Given the ease of collection, saliva has been proposed as a possible substitute to support testing at the population level. Here we describe the set-up of a laboratory, in an academic context, for the high-throughput screening of SARS-CoV-2 in the saliva from the community. A novel saliva collection device was designed to favour the safe and correct acquisition of the sample as well as the processivity of the downstream molecular analysis. To test the performance of the system,1025 paired saliva and nasopharyngeal samples were collected from individuals recruited at a public drive through testing facility and analysed in parallel. An overall moderate concordance (68%) between the two tests was found, with evidence that neither test can diagnose the infection in 100% of the cases. While the two tests performed equally well in symptomatic individuals, their discordance was mainly restricted to samples from convalescent individuals. The saliva test was at least as effective as NP swabs in asymptomatic individuals recruited for contact tracing. Our study, therefore, indicates that saliva testing can be a reliable tool for wide-scale COVID-19 screening in the community.