Seroprevalence of SARS-CoV-2 in blood donors from the Lodi Red Zone and adjacent Lodi metropolitan and suburban area.

OBJECTIVES: To define the seroprevalence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in blood donors (referred to the first lockdown area (Lodi Red-Zone) of the Lombardy region and in a contiguous area that was not included in the first lockdown); to define the agreement between a commercial serological assay and a reference microneutralization assay; and to evaluate the persistence of SARS-CoV-2 neutralizing antibodies in a cohort of blood donors. METHODS: Blood donors referred to the first lockdown area in Lombardy Region and the neighbouring area were analysed for SARS-CoV-2 IgG-specific antibodies during the period 18 March to 24 June 2020. Serum samples were analysed using both a chemiluminescent immunoassay (LIAISON® SARS-CoV-2 S1/S2 IgG, DiaSorin) for the quantitative characterization of SARS-CoV-2 anti-S1 and anti-S2 IgG antibodies and a neutralizing antibodies (NT-Abs) assay. RESULTS: In the period from 18 March to 24 June, 1922 blood donors were tested for the presence of SARS-CoV-2 IgG showing a prevalence of 378/1922 (19.7%). A subgroup of 1139 blood donors were tested in parallel with a SARS-CoV-2 IgG assay and a microneutralization assay showing a prevalence of 22.2% and 21.6%, respectively. SARS-CoV-2 IgG quantification was correlated with NT-Abs titres. In 78.2% of participants the NT-Abs titre was maintained, but in 15.8% it decreased by one four-fold dilution and in 6.0% it increased by one four-fold dilution. CONCLUSIONS: The duration of immunity of SARS-CoV-2 is crucial for the course of the pandemic and for this reason the monitoring of NT Abs is important. Despite a stable NT-Abs titre being observed in the majority of blood donors, our findings need to be validated in a long-term period of follow up.

SARS-CoV-2 Virologic and Immunologic Correlates in Patients with Olfactory and Taste Disorders

The main object of the study was to investigate the SARS-CoV-2 molecular and serological pattern in patients with mild symptoms including anosmia and ageusia. A cohort of 69 patients with olfactory and taste disorders (OTDs) were enrolled and prospectively monitored. Serological and molecular assays for the characterization of SARS-CoV-2 IgG and SARS-CoV-2 RNA, respectively, were performed at the time of enrolment and after 7 and 14 days. Patients were stratified according to the symptoms"onset. A total of 52 patients (75.4%) were diagnosed as COVID-19 positive being SARS-CoV-2 RNA and/or SARS-CoV-2 IgG positive. The remaining 17 (24.6%) were negative for COVID-19 and excluded from the analysis. We reported that only 34 out of 52 patients (65.4%) were positive for SARS-CoV-2 RNA. Moreover, the median time from onset of symptoms and enrolment was significantly higher in those patients with negative SARS-CoV-2 RNA in nasal swabs, suggesting that symptoms might last longer than SARS-CoV-2 replication. The great majority of patients (80%) developed SARS-CoV-2 IgG at three weeks after symptoms"onset while the detectability of SARS-CoV-2 RNA dramatically decreased over time, suggesting the crucial role of combination of molecular and serological assays for the diagnosis of COVID-19 in those patients reporting mild symptoms.

Clinical and Analytical Performance of an Automated Serological Test That Identifies S1/S2-Neutralizing IgG in COVID-19 Patients Semiquantitatively.

In the coronavirus (CoV) disease 2019 (COVID-19) pandemic, highly selective serological testing is essential to define exposure to severe acute respiratory syndrome CoV 2 (SARS-CoV-2). Many tests have been developed, yet with variable speeds to first results, and are of unknown quality, particularly when considering the prediction of neutralizing capacity. The LIAISON SARS-CoV-2 S1/S2 IgG assay was designed to measure antibodies against the SARS-CoV-2 native S1/S2 proteins in a standardized automated chemiluminescence assay. The clinical and analytical performances of the test were validated in an observational study using residual samples (>1,500) with a positive or negative COVID-19 diagnosis. The LIAISON SARS-CoV-2 S1/S2 IgG assay proved to be highly selective and specific and offered semiquantitative measures of serum or plasma levels of anti-S1/S2 IgG with neutralizing activity. The assay's diagnostic sensitivities were 91.3% and 95.7% at >5 or ≥15 days from diagnosis, respectively, and 100% when assessed against a neutralizing assay. The assay's specificity ranged between 97% and 98.5%. The average imprecision of the assay was a <5% coefficient of variation. Assay performance at 2 different cutoffs was evaluated to optimize predictive values. The automated LIAISON SARS-CoV-2 S1/S2 IgG assay brings efficient, sensitive, specific, and precise serological testing to the laboratory, with the capacity to test large amounts of samples per day; first results are available within 35 min, with a throughput of 170 tests/hour. The semiquantitative results provided by the test also associate with the presence of neutralizing antibodies and may provide a useful tool for the large-scale screening of convalescent-phase plasma for safe therapeutic use.