ABSTRACT
Background: We evaluate the diagnostic performance of dried blood microsampling combined with a high-throughput microfluidic nano-immunoassay (NIA) for the identification of anti-SARS-CoV-2 Spike IgG seropositivity. Methods: We conducted a serological study among 192 individuals with documented prior SARS-CoV- 2 infection and 44 SARS-CoV-2 negative individuals. Participants with prior SARS-CoV-2 infection had a long interval of 11 months since their qRT-PCR positive test. Serum was obtained after venipuncture and tested with an automated electrochemiluminescence anti-SARS-CoV-2 S total Ig reference assay, a commercial ELISA anti-S1 IgG assay, and the index test NIA. 109 participants from the positive co- hort and 44 participants from the negative cohort also participated in capillary blood collection using three microsampling devices: Mitra, repurposed glucose test strips, and HemaXis. Samples were dried, shipped by regular mail, extracted, and measured with NIA. Findings: Using serum samples, we achieve a clinical sensitivity of 98.33% and specificity of 97.62% on NIA, affirming the high performance of NIA in participants 11 months post infection. Combining microsampling with NIA, we obtain a clinical sensitivity of 95.05% using Mitra, 61.11% using glucose test strips, 83.16% using HemaXis, and 91.49% for HemaXis after automated extraction, without any drop in specificity. Interpretation: High sensitivity and specificity was demonstrated when testing micro-volume capillary dried blood samples using NIA, which is expected to facilitate its use in large-scale studies using home- based sampling or samples collected in the field. Funding: Swiss National Science Foundation NRP 78 Covid-19 grant 198412 and Private Foundation of the Geneva University Hospital.
Subject(s)
Severe Acute Respiratory Syndrome , COVID-19ABSTRACT
Background Twenty-one months into the pandemic, the extent to which young children get infected and transmit SARS-CoV-2 in school settings remains controversial, in particular with variants of concern. We report a prospective epidemiological, virological and serological investigation of a SARS-CoV-2 outbreak in a primary school in Geneva, Switzerland, in April-May 2021. Methods This outbreak investigation is part of a longitudinal, prospective, primary school-based surveillance study (SEROCoV-Schools). It involved repeated testing of pupils and teachers and household members of participants who tested positive. Rapid antigen tests and/or real-time reverse transcription polymerase chain reaction were performed at Day 0-2 and Day 5-7; serologies on dried capillary blood samples were performed at Day 0-2 and Day 30. Contact tracing interviews and SARS-CoV-2 whole genome sequencing were carried out for positive cases. Results This SARS-CoV-2 outbreak caused by the Alpha variant involved 20 children aged 4 to 6 years from 4 classes, 2 teachers and 3 household members. Infection attack rates were between 11.8 and 62.0% among pupils from the 4 classes, 22.2% among teachers and 0% among non-teaching staff. Secondary attack rate among household members was 10.7%. Symptoms were reported by 63% of infected children, 100% of teachers and 66.7% of household members. All analysed sequences but one showed 100% identity. Serological tests detected 8 seroconversions unidentified by SARS-CoV-2 virological tests. Conclusions This study confirmed child-to-child and child-to-adult transmission of the infection. SARS-CoV-2 can spread rapidly between children and adults in school settings, and is thereby introduced into households. Effective measures to limit transmission in schools have the potential to reduce the overall community circulation.
ABSTRACT
Novel technologies are needed to facilitate large-scale detection and quantification of SARS-CoV-2 specific antibodies in human blood samples. Such technologies are essential to support seroprevalence studies, vaccine clinical trials, and to monitor quality and duration of immunity. We developed a microfluidic nano-immunnoassay for the detection of anti-SARS-CoV-2 IgG antibodies in 1024 samples per device. The method achieved a specificity of 100% and a sensitivity of 98% based on the analysis of 289 human serum samples. To eliminate the need for venipuncture, we developed low-cost, ultra-low volume whole blood sampling methods based on two commercial devices and repurposed a blood glucose test strip. The glucose test strip permits the collection, shipment, and analysis of 0.6 L whole blood easily obtainable from a simple fingerprick. The nano-immunoassay platform achieves high-throughput, high sensitivity and specificity, negligible reagent consumption, and a decentralized and simple approach to blood sample collection. We expect this technology to be immediately applicable to current and future SARS-CoV-2 related serological studies and to protein biomarker diagnostics in general.