ABSTRACT
Background: Accurate, affordable, and rapid point-of-care (PoC) diagnostics are critical to the global control and management of the COVID-19 pandemic. The current standard for accurate diagnosis of SARS-CoV-2 is laboratory-based reverse transcription polymerase chain reaction (RT-PCR). Here, we report a preliminary prospective performance evaluation of the QuantuMDx Q-POC SARS CoV-2 RT-PCR assay. Methods: Between November 2020 and March 2021, we obtained 49 longitudinal nose and throat swabs from 29 individuals hospitalised with RT-PCR confirmed COVID-19 at St Georges' NHS Foundation Trust, London (UK). In addition, we obtained 101 mid nasal swabs from healthy volunteers in June 2021. We then used these samples to evaluate the Q-POC SARS-CoV-2 RT-PCR assay. The primary analysis was to compare the sensitivity and specificity of the Q-POC test against a reference laboratory-based RT-PCR assay. Results: The overall sensitivity of the Q-POC test compared with the reference test was 96.88% (83.78%- 99.92% CI) for a cycle threshold (Ct) cut-off value for the reference test of 35 and 80.00% (64.35% to 90.95% CI) without altering the reference test's Ct cut-off value of 40. Conclusions: The Q-POC test is a sensitive, specific and rapid point-of-care test for SARS-CoV-2 at a reference Ct cut-off value of 35. The Q-POC test provides an accurate and afforda-ble option for RT-PCR at point-of-care without the need for sample pre-processing and laboratory handling. The Q-POC test would enable rapid diagnosis and clinical triage in acute care and other settings.
Subject(s)
COVID-19ABSTRACT
Severe acute respiratory coronavirus 2 (SARS-CoV-2) has spread globally since its emergence in 2019. Most SARS-CoV-2 infections generate immune responses leading to rising levels of immunoglobulins (Ig) M, A and G which can be detected using diagnostic tests including enzyme-linked immunosorbent assays (ELISA). Whilst implying previous SARS-CoV-2 infection, the detection of Ig by ELISA does not guarantee the presence of neutralising antibodies (NAb) that can prevent the virus infecting cells. Plaque reduction neutralisation tests (PRNT) detect NAb but are not amenable to mass testing as they take several days and require use of viable SARS-CoV-2 in high biocontainment laboratories. We evaluated the ability of IgG and IgM ELISAs targeting SARS-CoV-2 spike subunit 1 (S1) and nucleocapsid protein (NP) at predicting the presence and magnitude of NAb determined by PRNT. SARS-CoV-2 IgG ELISA correlated well with NAb and was highly sensitive (93.8% [95% CI 79.2–99.2]) and specific (88.9% [95% CI 51.8–99.7%]) at predicting the presence of NAb. There was not a strong correlation between IgM ELISA and PRNT result. IgG ELISA provides a useful, high throughput method of predicting the presence of neutralising antibodies, with higher ELISA results increasing the likelihood of having a greater NAb titre.
Subject(s)
COVID-19ABSTRACT
We report dynamics of seroconversion to SARS-CoV-2 infections detected by IgG ELISA in 177 individuals diagnosed by RT-PCR. Longitudinal analysis identifies 2-8.5% of individuals who do not seroconvert even weeks after infection. They are younger than seroconverters who have increased co-morbidity and higher inflammatory markers such as C-Reactive Protein. Higher antibody responses are associated with non-white ethnicity. Antibody responses do not decline during follow up almost to 2 months. Serological assays increase understanding of disease severity. Their application in regular surveillance will clarify the duration and protective nature of humoral responses to SARS-CoV-2.