Qualitative and quantitative detection of SARS-CoV-2 antibodies from dried blood spots.

INTRODUCTION: Dried blood spot (DBS) sampling is a minimally invasive method for specimen collection with potential multifaceted uses, particularly for serosurveillance of previous SARS-CoV-2 infection. In this study, we assessed DBS as a potential specimen type for assessing IgG and total (including IgG and IgM) antibodies to SARS-CoV-2 in vaccinated and naturally infected patients. METHODS: Six candidate buffers were assessed for eluting blood from DBS cards. The study utilized one hundred and five paired plasma specimens and DBS specimens from prospectively collected SARS-CoV-2 vaccinated individuals, remnants from those with PCR confirmed SARS-CoV-2 infections, or remnants from those without history of infection or vaccination. All specimens were tested with the Siemens SARS-CoV-2 total assay (COV2T) or IgG assay (sCOVG). RESULTS: The lowest backgrounds were observed with water and PBS, and water was used for elution. Relative to plasma samples, DBS samples had a positive percent agreement (PPA) of 94.4% (95% CI: 94.9-100%) for COV2T and 79.2 (68.4-87.0) for sCOVG using the manufacturer's cutoff. The NPA was 100 % (87.1-100.0 and 85.13-100) for both assays. Dilution studies revealed 100% (95% CI: 90.8-100%) qualitative agreement between specimen types on the COV2T assay and 98.0% (88.0-99.9%) with the sCOVG using study defined cutoffs. CONCLUSION: DBS specimens demonstrated high PPA and NPA relative to plasma for SARS-CoV-2 serological testing. Our data support feasibility of DBS sampling for SARS-CoV-2 serological testing.

Seroprevalence of severe acute respiratory coronavirus virus 2 (SARS-CoV-2) antibodies among healthcare personnel in the Midwestern United States, September 2020-April 2021.

Objective: To determine the prevalence of severe acute respiratory coronavirus virus 2 (SARS-CoV-2) IgG nucleocapsid (N) antibodies among healthcare personnel (HCP) with no prior history of COVID-19 and to identify factors associated with seropositivity. Design: Prospective cohort study. Setting: An academic, tertiary-care hospital in St. Louis, Missouri. Participants: The study included 400 HCP aged ≥18 years who potentially worked with coronavirus disease 2019 (COVID-19) patients and had no known history of COVID-19; 309 of these HCP also completed a follow-up visit 70-160 days after enrollment. Enrollment visits took place between September and December 2020. Follow-up visits took place between December 2020 and April 2021. Methods: At each study visit, participants underwent SARS-CoV-2 IgG N-antibody testing using the Abbott SARS-CoV-2 IgG assay and completed a survey providing information about demographics, job characteristics, comorbidities, symptoms, and potential SARS-CoV-2 exposures. Results: Participants were predominately women (64%) and white (79%), with median age of 34.5 years (interquartile range [IQR], 30-45). Among the 400 HCP, 18 (4.5%) were seropositive for IgG N-antibodies at enrollment. Also, 34 (11.0%) of 309 were seropositive at follow-up. HCP who reported having a household contact with COVID-19 had greater likelihood of seropositivity at both enrollment and at follow-up. Conclusions: In this cohort of HCP during the first wave of the COVID-19 pandemic, ∼1 in 20 had serological evidence of prior, undocumented SARS-CoV-2 infection at enrollment. Having a household contact with COVID-19 was associated with seropositivity.

Serial cardiac biomarkers for risk stratification of patients with COVID-19.

OBJECTIVES: Several studies have demonstrated an association between elevated cardiac biomarkers and adverse outcomes in patients with COVID-19. However, the prognostic and predictive capability of a multimarker panel in a prospectively collected, diverse "all-comers" COVID-19 population has not been fully elucidated. DESIGN & METHODS: We prospectively assessed high sensitivity cardiac troponin I (hsTnI), NT-pro B-type Natriuretic Peptide (NT-proBNP), Galectin-3 (Gal-3), and procalcitonin (PCT) in 4,282 serial samples from 358 patients admitted with symptomatic, RT-PCR confirmed SARS-CoV-2 infection. Outcomes examined were 30-day in-hospital mortality and requirement for intubation within 10 days. RESULTS: Baseline hsTnI had the highest AUC for predicting 30-day mortality (0.81; 95% CI, 0.73-0.88), followed by NT-proBNP (0.80; 0.74-0.86), PCT (0.77; 0.70-0.84), and Gal-3 (0.68; 0.60-0.76). HsTnI < 3.5 ng/L at baseline identified patients at low risk for in-hospital mortality (NPV 95.9%, sensitivity 97.3%) and 10-day intubation (NPV 90.4%, sensitivity 88.5%). Continuous, log-2 increases in troponin concentration were associated with reduced survival (p < 0.001) on Kaplan-Meier curves and increased risk of 30-day mortality: HR 1.26 (1.16-1.37) in univariate and 1.19 (1.03-1.4) in multivariate models. Time-varying doubling of concentrations of hsTnI and Gal-3 were associated with increased risk of 30-day mortality (adjusted HR 1.21, 1.06-1.4, and 1.92, 1.40-2.6). CONCLUSION: HsTnI, NT-proBNP, Gal-3, and PCT are elevated at baseline in patients that have worse outcomes from COVID-19. HsTnI was the only independent predictor of 30-day mortality and intubation. Time-varying, doubling in hsTnI and Gal-3 further aided in prognostication of adverse outcomes. These results support the use of hsTnI for triaging patients with COVID-19.

Plasmonic Fluor-Enhanced Antigen Arrays for High-Throughput, Serological Studies of SARS-CoV-2.

Serological testing for acute infection or prior exposure is critical for patient management and coordination of public health decisions during outbreaks. Current methods have several limitations, including variable performance, relatively low analytical and clinical sensitivity, and poor detection due to antigenic drift. Serological methods for SARS-CoV-2 detection for the ongoing COVID-19 pandemic suffer from several of these limitations and serves as a reminder of the critical need for new technologies. Here, we describe the use of ultrabright fluorescent reagents, Plasmonic Fluors, coupled with antigen arrays that address a subset of these limitations. We demonstrate its application using patient samples in SARS-CoV-2 serological assays. In our multiplexed assay, SARS-CoV-2 antigens were spotted into 48-plex arrays within a single well of a 96-well plate and used to evaluate remnant laboratory samples of SARS-CoV-2 positive patients. Signal-readout was performed with Auragent Bioscience's Empower microplate reader, and microarray analysis software. Sample volumes of 1 µL were used. High sensitivity of the Plasmonic Fluors combined with the array format enabled us to profile patient serological response to eight distinct SARS-CoV-2 antigens and evaluate responses to IgG, IgM, and IgA. Sensitivities for SARS-CoV-2 antigens during the symptomatic state ranged between 72.5 and 95.0%, specificity between 62.5 and 100%, and the resulting area under the curve values between 0.76 and 0.97. Together, these results highlight the increased sensitivity for low sample volumes and multiplex capability. These characteristics make Plasmonic Fluor-enhanced antigen arrays an attractive technology for serological studies for the COVID-19 pandemic and beyond.

Antibodies in healthcare personnel following severe acute respiratory syndrome coronavirus virus 2 (SARS-CoV-2) infection.

In a prospective cohort of healthcare personnel (HCP), we measured severe acute respiratory syndrome coronavirus virus 2 (SARS-CoV-2) nucleocapsid IgG antibodies after SARS-CoV-2 infection. Among 79 HCP, 68 (86%) were seropositive 14-28 days after their positive PCR test, and 54 (77%) of 70 were seropositive at the 70-180-day follow-up. Many seropositive HCP (95%) experienced an antibody decline by the second visit.

Predictors of humoral response to SARS-CoV-2 mRNA vaccine BNT162b2 in patients receiving maintenance dialysis.

Objective: Patients on dialysis are at high risk for severe COVID-19 and associated morbidity and mortality. We examined the humoral response to SARS-CoV-2 mRNA vaccine BNT162b2 in a maintenance dialysis population. Design: Single-center cohort study. Setting and participants: Adult maintenance dialysis patients at 3 outpatient dialysis units of a large academic center. Methods: Participants were vaccinated with 2 doses of BNT162b2, 3 weeks apart. We assessed anti-SARS-CoV-2 spike antibodies (anti-S) ∼4-7 weeks after the second dose and evaluated risk factors associated with insufficient response. Definitions of antibody response are as follows: nonresponse (anti-S level, <50 AU/mL), low response (anti-S level, 50-839 AU/mL), and sufficient response (anti-S level, ≥840 AU/mL). Results: Among the 173 participants who received 2 vaccine doses, the median age was 60 years (range, 28-88), 53.2% were men, 85% were of Black race, 86% were on in-center hemodialysis and 14% were on peritoneal dialysis. Also, 7 participants (4%) had no response, 27 (15.6%) had a low response, and 139 (80.3%) had a sufficient antibody response. In multivariable analysis, factors significantly associated with insufficient antibody response included end-stage renal disease comorbidity index score ≥5 and absence of prior hepatitis B vaccination response. Conclusions: Although most of our study participants seroconverted after 2 doses of BNT162b2, 20% of our cohort did not achieve sufficient humoral response. Our findings demonstrate the urgent need for a more effective vaccine strategy in this high-risk patient population and highlight the importance of ongoing preventative measures until protective immunity is achieved.