ABSTRACT
ObjectivesThe aim of this study was to assess changes in exposure and prevalence of SARS-CoV-2 infection during the first months of emergence of Omicron variant in the Greater Helsinki area, Finland. MethodsA prospective seroepidemiological survey of SARS-CoV-2 was conducted on 1,600 serum specimens sent to Helsinki University Hospital Laboratory (HUSLAB) for HIV serology between 15 November 2021 and 6 March 2022 (calendar weeks 46/2021 - 9/2022). For each calendar week, 100 serum specimens were randomly selected and analysed for SARS-CoV-2 IgG antibodies against nucleocapsid (N) and spike 1 (S1) protein with Abbott SARS-CoV-2 IgG (N protein) and SARS-CoV-2 IgG II Quant (S protein) tests, respectively. ResultsThe prevalence of N antibodies increased from 5.2% (weeks 46-50/2021) to 28.2% (weeks 5-9/2022) during the study period. The proportion of seronegative samples as well as anti-N negative, anti-S1 positive samples decreased correspondingly from 11.6% to 3.8%, and 84.2% to 68.2%, respectively. Anti-N positive samples that were anti-S1 negative only began to appear as of week 2/2022. ConclusionsA rapid increase in the N antibody prevalence was observed over the study period, suggesting a high transmission rate. A substantial proportion of COVID-19 cases remained undiagnosed during the emergence of Omicron variant in the Greater Helsinki Area, Finland.
ABSTRACT
SARS-CoV-2 RNA can be detected in respiratory samples for weeks or even months after onset of COVID-19 disease. Therefore, one of the diagnostic challenges of PCR positive cases is differentiating between acute COVID-19 disease and convalescent phase. Recently, the presence of SARS-CoV-2 nucleocapsid antigen in serum samples of COVID-19 patients was published [Le Hingrat et al. Detection of SARS-CoV-2 N-antigen in blood during acute COVID-19 provides a sensitive new marker and new testing alternatives, Clinical Microbiology and Infection, 2020]. Our study aimed to characterize the analytical specificity and sensitivity of an enzyme-linked immunosorbent assay (Salocor SARS-CoV-2 Antigen Quantitative Assay Kit(C) (Salofa Ltd, Salo, Finland)) for the detection of SARS-CoV-2 antigen in serum, and to characterize the kinetics of antigenemia. The evaluation material included a negative serum panel of 155 samples, and 126 serum samples from patients with PCR-confirmed COVID-19. The specificity of the Salocor SARS-CoV-2 serum N antigen test was 98.0%. In comparison with simultaneous positive PCR from upper respiratory tract (URT) specimens, the test sensitivity was 91.7%. In a serum panel in which the earliest serum sample was collected two days before the collection of positive URT specimen, and the latest 48 days after (median 1 day post URT sample collection), the serum N antigen test sensitivity was 94% within 14 days post onset of symptoms. The antigenemia resolved approximately two weeks after the onset of disease and diagnostic PCR. The combination of simultaneous SARS-CoV-2 antigen and antibody testing appeared to provide useful information for the timing of COVID-19. Our results suggest that SARS-CoV-2 N-antigenemia may be used as a diagnostic marker in acute COVID-19.
ABSTRACT
Laboratory registry data (80,791 specimens, 70,517 individuals) was used to characterise age- and sex-specific SARS-CoV-2 RT-PCR sampling frequency and positivity rate, and laboratory capacity building in Greater Helsinki, Finland during February-June 2020. While the number of positive cases was similar in males and females, the positivity rate was significantly higher in males. The highest incidence/100,000 was observed in those aged [≥]80 years. The proportion of young adults in positive cases increased in late May 2020.
ABSTRACT
There is an urgent need for reliable high-throughput serological assays for the management of the ongoing COVID-19 pandemic. Preferably, the performance of serological tests for a novel virus should be determined with clinical specimens against a gold standard, i.e. virus neutralisation. We evaluated specificity and sensitivity of six commercial immunoassays for the detection of SARS-CoV-2 IgG, IgA and IgM antibodies, including four automated assays [Abbott SARS-COV-2 IgG (CE marked), Diasorin Liaison(R) SARS-CoV-2 S1/S2 IgG (research use only), and Euroimmun SARS-CoV-2 IgG and IgA (CE marked)], and two rapid lateral flow (immunocromatographic) tests [Acro Biotech 2019-nCoV IgG/IgM (CE marked) and Xiamen Biotime Biotechnology SARS-CoV-2 IgG/IgM (CE marked)] in comparison with a microneutralisation test (MNT). Two specimen panels from serum samples sent to Helsinki University Hospital Laboratory (HUSLAB) were compiled: the patient panel included sera from PCR confirmed COVID-19 patients, and the negative panel included sera sent for screening of autoimmune diseases and respiratory virus antibodies in 2018 and 2019. The MNT was carried out for all COVID-19 samples (70 serum samples, 62 individuals) and for 53 samples from the negative panel. Forty-one out of 62 COVID-19 patients showed neutralising antibodies with median of 11 days (range 3-51) after onset of symptoms. The specificity and sensitivity values of the commercial tests against MNT, respectively, were as follows: 95.1%/80.5% (Abbott Architect SARS-CoV-2 IgG), 94.9%/43.8% (Diasorin Liaison SARS-CoV-2 IgG), 68.3%/87.8% (Euroimmun SARS-CoV-2 IgA), 86.6%/70.7% (Euroimmun SARS-CoV-2 IgG), 74.4%/56.1% (Acro 2019-nCoV IgG), 69.5%/46.3% (Acro 2019-nCoV IgM), 97.5%/71.9% (Xiamen Biotime SARS-CoV-2 IgG), and 88.8%/81.3% (Xiamen Biotime SARSCoV-2 IgM). This study shows variable performance values. Laboratories should carefully consider their testing process, such as a two-tier approach, in order to optimize the overall performance of SARS-CoV-2 serodiagnostics.
