Genomic epidemiology of SARS-CoV-2 transmission lineages in Ecuador (preprint)

Characterisation of SARS-CoV-2 genetic diversity through space and time can reveal trends in virus importation and domestic circulation, and permit the exploration of questions regarding the early transmission dynamics. Here we present a detailed description of SARS-CoV-2 genomic epidemiology in Ecuador, one of the hardest hit countries during the early stages of the COVID-19 pandemic. We generate and analyse 160 whole genome sequences sampled from all provinces of Ecuador in 2020. Molecular clock and phylgeographic analysis of these sequences in the context of global SARS-CoV-2 diversity enable us to identify and characterise individual transmission lineages within Ecuador, explore their spatiotemporal distributions, and consider their introduction and domestic circulation. Our results reveal a pattern of multiple international importations across the country, with apparent differences between key provinces. Transmission lineages were mostly introduced before the implementation of non-pharmaceutical interventions (NPIs), with differential degrees of persistence and national dissemination.

Impaired performance of SARS-CoV-2 antigen-detecting rapid tests at elevated temperatures (preprint)

Rapid antigen-detecting tests (Ag-RDTs) can complement molecular diagnostics for COVID-19. The recommended temperature for storage of SARS-CoV-2 Ag-RDTs ranges between 5-30°C. In many countries that would benefit from SARS-CoV-2 Ag-RDTs, mean temperatures exceed 30°C. We assessed analytical sensitivity and specificity of eleven commercially available SARS-CoV-2 Ag-RDTs using different storage and operational temperatures, including (i) long-term storage and testing at recommended conditions, (ii) recommended storage conditions followed by 10 minutes exposure to 37°C and testing at 37°C and (iii) 3 weeks storage followed by testing at 37°C. The limits of detection of SARS-CoV-2 Ag-RDTs under recommended conditions ranged from 8.2×10 5 -7.9×10 7 genome copies/ml of infectious SARS-CoV-2 cell culture supernatant. Despite long-term storage at recommended conditions, 10 minutes pre-incubation of Ag-RDTs and testing at 37°C resulted in about ten-fold reduced sensitivity for 46% of SARS-CoV-2 Ag-RDTs, including both Ag-RDTs currently listed for emergency use by the World Health Organization. After 3 weeks of storage at 37°C, 73% of SARS-CoV-2 Ag-RDTs exhibited about ten-fold reduced sensitivity. Specificity of SARS-CoV-2 Ag-RDTs using cell culture-derived human coronaviruses HCoV-229E and HCoV-OC43 was not affected by storage and testing at 37°C. In summary, short- and long-term exposure to elevated temperatures likely impairs sensitivity of several SARS-CoV-2 Ag-RDTs that may translate to false-negative test results at clinically relevant virus concentrations compatible with inter-individual transmission. Ensuring appropriate transport and storage conditions, and development of tests that are more robust across temperature fluctuations will be important for accurate use of SARS-CoV-2 Ag-RDTs in tropical settings.