COVID-19, caused by the novel coronavirus SARS-CoV-2, has spread worldwide and put most of the world under lockdown. Despite that there have been emergently approved vaccines for SARS-CoV-2, COVID-19 cases, hospitalizations, and deaths have remained rising. Thus, rapid diagnosis and necessary public health measures are still key parts to contain the pandemic. In this study, the colorimetric isothermal nucleic acid amplification tests (iNAATs) for SARS-CoV-2 detection based on loop-mediated isothermal amplification (LAMP), cross-priming amplification (CPA), and polymerase spiral reaction (PSR) were designed and evaluated. The three methods showed the same limit of detection (LOD) value of 1 copy of the targeted gene per reaction. However, for the direct detection of SARS-CoV-2 genomic-RNA, LAMP outperformed both CPA and PSR, exhibiting the LOD value of roughly 43.14 genome copies/reaction. The results can be read with the naked eye within 45 minutes, without cross-reactivity to closely related coronaviruses. Moreover, the direct detection of SARS-CoV-2 RNA in simulated patient specimens by iNAATs was also successful. Finally, the ready-to-use lyophilized reagents for LAMP reactions were shown to maintain the sensitivity and LOD value of the liquid assays. The results indicate that the colorimetric lyophilized LAMP kit developed herein is highly suitable for detecting SARS-CoV-2 nucleic acids at point-of-care.

: Relatively little is known about the seroprevalence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) IgG antibodies and COVID-19-related behaviors in the general population in Vietnam, where the first case of COVID-19 was detected on January 22, 2020. We surveyed a group of 885 blood donors at community blood donation sessions in Ho Chi Minh City from August 27 to November 7, 2020. Blood was collected to test for SARS-CoV-2 IgG antibodies using the plaque reduction neutralization test. We adjusted the seroprevalence by weight for ages 18 to 59 years old obtained from the 2019 population census. The weighted seroprevalence estimate for SARS-CoV-2 neutralizing IgG antibodies was 0.20% (95% CI, 0.05–0.81). Reports of usually or always using a mask in public places were observed at high levels of 28.6% and 67.5%, respectively. The percentages of usually or always washing hands with soap or disinfecting with hand sanitizer after touching items in public places were 48.0% and 37.6%, respectively. Although our findings suggest undocumented exposure to the virus, the seroprevalence of SARS-CoV-2 IgG antibodies among blood donors was low in this city.

Background: There is a shortage of chemical reagents for severe acute respiratory syndrome - coronavirus 2 ( SARS-CoV-2 ) diagnosis and a surge of SARS-CoV-2 cases, especially in limited-resource settings. Therefore, the combination of an optimal assay kit is necessary. Methods: We compared the ability to screen SARS-CoV-2 among three primer-probe sets in two different master mixes, Invitrogen™ SuperScript™ III One-Step RT-PCR and LightCycler Multiplex RNA Virus Master. Results: The assay with TIB-Molbiol, IDT, and Phu Sa sets for LightCycler Multiplex RNA Virus Master or Invitrogen™ SuperScript™ III One-Step RT-PCR showed positive results from a single reaction of triplicate in the three days of 4.8 copies per reaction. R-squared and amplification efficiency were 0.97 and ranged from 107 to 108%, respectively. Conclusions: Our findings indicated that TIB-Molbiol, IDT, and Phu Sa primer-probe sets could be beneficial for the laboratory screening of SARS-CoV-2 by RT-qPCR assay of E gene. There is a need to consider the combination of these reagent sets as a new strategy to increase the testing capacity of screening programs for COVID-19.