Subsequently, samples within 10% of the 20% inhibition cut-off value were repeated in duplicate, with the final qualitative result determined by the majority result

Subsequently, samples within 10% of the 20% inhibition cut-off value were repeated in duplicate, with the final qualitative result determined by the majority result.18 The Abbott and DiaSorin assays were also tested against serum samples obtained from healthcare workers (HCW) at the Royal Melbourne Hospital at different time periods during the Victorian COVID-19 outbreaks. period was highest for the Roche at 95.2100% (95% CI 81.0100%), then the DiaSorin at 88.1100% (95% CI 76.0100%), followed by the Abbott 68.2100% (95% CI 53.4100%). Sensitivity of the Abbott assay fell from approximately 5 months; on this assay paired serum samples for 45 participants showed a significant drop in the signal-to-cut-off ratio and 10 sero-reversion events. When used in clinical practice, all samples testing positive by both DiaSorin and Abbott assays were BTRX-335140 confirmed as true positive results. In this low prevalence setting, despite high laboratory specificity, the positive predictive value of a single positive assay was low. Comprehensive validation of serological assays is necessary to determine the optimal assay for each diagnostic setting. In this low prevalence setting we found implementation of two assays with different antibody targets maximised sensitivity and specificity, with confirmatory testing necessary for any sample which was positive in only one assay. Key words:COVID-19 serology, Abbott, DiaSorin, Roche, clinical validation == Introduction == BTRX-335140 Following the emergence and spread of the novel coronavirus 2019, SARS-CoV-2, a range of diagnostic assays BTRX-335140 have been developed.1Real-time PCR (RT-PCR) testing for SARS-CoV-2 RNA is the gold standard for diagnosis of acute infection, with serological testing reserved for specific scenarios (e.g., epidemiological surveillance; resolving indeterminate RT-PCR findings).2A range of commercial serological assays are now available, with the majority targeting either the nucleocapsid antigen (N), the spike protein (S), or a component of the spike protein such as the receptor binding domain (RBD).3The RBD is Rabbit polyclonal to ARHGAP20 the distal area of the spike protein that binds with host angiotensin-converting enzyme 2 receptors (ACE2-R) to facilitate viral cell entry.3Antibodies which recognise this region are more likely to be neutralising, which has been supported by good correlation between S1 or RBD targeted antibodies and neutralisation assays.4,5To date, however, the optimal target antigen for commercial diagnostic assays has not yet been determined, and may vary depending on: (i) whether the purpose of testing is to determine exposure to the virus (non-neutralising or neutralising antibodies) or putative immunity (neutralising antibodies), (ii) at what time point sampling occurs following infection, and (iii) the vaccination status of the patient. Understanding the performance characteristics of the assays in a number of different settings, and with different clinical cohorts, is important in designing testing algorithms relevant for the local population and in providing accurate clinical interpretation of results for clinicians. The average time to seroconversion following SARS-CoV-2 symptom onset is 1015 days, with the majority of patients seroconverting by 21 days.3,6Antibody titres may correlate with severity of illness, with lower titres observed in patients who remain asymptomatic throughout their infection.7,8The longevity of the antibody response to SARS-CoV-2 is unknown, although based on studies of the related seasonal beta-coronaviruses as well as SARS-CoV-1 and MERS-CoV, is expected to last between 1 and 5 years.3,6,9Antibody titres against SARS-CoV-2 N protein have been shown to rise earlier than those directed against the S protein following infection, and recent evidence suggests that the half-life of anti-N antibodies may be shorter.10,11 At the time of writing Australia has successfully controlled the COVID-19 pandemic; as of 24 November 2020, COVID-19 cases are sporadic (due to international importation in quarantined travellers) or associated with small community clusters.12The state of Victoria has experienced the largest number of COVID-19 cases, reporting 73% of the 27,835 cases confirmed in Australia since the first case on 26 January 2020.12,13Despite two waves of infections, first in March to April and then again between June to September, the period prevalence of COVID-19 for Victoria (0.4%) remains low compared to international reports.13Longitudinal sampling of RT-PCR confirmed COVID-19 cases in Victoria therefore likely reflects the dynamics of SARS-CoV-2 antibody generation following a single exposure to the virus. To date, there are few published data on the longitudinal performance characteristics of serological assays for COVID-19. Accordingly, we undertook a laboratory validation of three commercial assays, the Architect SARS-CoV-2 IgG (Abbott, USA), Liaison SARS-CoV-2 S1/S2 IgG (DiaSorin, Italy) and Cobas Elecsys Anti-SARS-CoV-2 (Roche, Switzerland), using sera from RT-PCR SARS-CoV-2 BTRX-335140 positive cases. Sera were further characterised by a surrogate virus neutralisation assay (sVNT) or an in-house microneutralisation assay. Longitudinal performance post-infection was determined by serial testing of a cohort of individuals infected in wave one.