Implementation of rapid SARS-CoV-2 antigenic testing in a laboratory without access to molecular methods:Experiences of a general hospital

Background: The COVID-19 Ag (Antigen) Respi-Strip assay is a new immunochromatographic diagnostic tool recently available for antigenic diagnosis of SARS-CoV-2. The proposed sensitivity is not higher than 60 %, but its high specificity allows both quick decisions for the management of patients and confirmation by molecular diagnosis for only negative tests. However, from the first tests performed, we suspected that the sensitivity observed with routine use was much lower than that announced by the manufacturer. Materials and methods: Over a period of one month, we compared the negative results obtained with the COVID-19 Ag Respi-Strip kit with those obtained from qRT-PCR performed in a laboratory qualified for the molecular diagnosis of SARS-CoV-2. All samples tested were naso-pharyngeal smears from UTM-RT medium. Results: Of 774 patients tested, 714 negative samples were sent for confirmation, and 159 were found to be positive by qRT-PCR. The median positive percentage agreement was 23.9 % (95 % CI: 14.2 %–38.2 %). The Cohen's kappa score was 0.35. Conclusion: Using this immunochromatographic assay as a triage test did not significantly reduce the number of samples outsourced for COVID-19 confirmation by qRT-PCR. In addition, even if the turn-around time is short, the assay is completely manual, which is not suitable for large volumes of routine samples. The sensitivity of this rapid test is poor, and improvements are needed to enhance its performance.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Source separation and distributed sensing: The key of an efficient monitoring

International audienceAs a complement to classical sensors, Distributed Optical Fiber Sensors now play a prominent role in several engineering fields and act as an antenna array. Depending of the devices used (Raman, Rayleigh, or Brillouin scattering), measurement records depend on temperature, strain, or pressure profile. As the wanted signal is often hidden by noise and other undesired sources, we can express the problem as a source separation problem. In this paper, we show that with the help of recent techniques based on data decomposition and source separation (PCA, ICA, NMF techniques) from the virtual antenna, we can accurately identify water leakages from a noisy Raman spectra or a strain profile from Brillouin spectra with a spatial resolution of 1cm instead of 1 meter for classical devices

Enhancement of an Optical Fiber Sensor: Source Separation Based on Brillouin Spectrum

International audienceDistributed optical fiber sensors have gained an increasingly prominent role in structural-health monitoring. These are composed of an optical fiber cable in which a light impulse is launched by an opto-electronic device. The scattered light is of interest in the spectral domain: the spontaneous Brillouin spectrum is centered on the Brillouin frequency, which is related to the local strain and temperature changes in the optical fiber. When coupled with an industrial Brillouin optical time-domain analyzer (B-OTDA), an optical fiber cable can provide distributed measurements of strain and/or temperature, with a spatial resolution over kilometers of 40 cm. This paper focuses on the functioning of a B-OTDA device, where we address the problem of the improvement of spatial resolution. We model a Brillouin spectrum measured within an integration base of 1 m as the superposition of the elementary spectra contained in the base. Then, the spectral distortion phenomenon can be mathematically explained: if the strain is not constant within the integration base, the Brillouin spectrum is composed of several elementary spectra that are centered on different local Brillouin frequencies. We propose a source separation methodology approach to decompose a measured Brillouin spectrum into its spectral components. The local Brillouin frequencies and amplitudes are related to a portion of the integration base where the strain is constant. A layout algorithm allows the estimation of a strain profile with new spatial resolution chosen by the user. Numerical tests enable the finding of the optimal parameters, which provides a reduction to 1 cm of the 40-cm spatial resolution of the B-OTDA device. These parameters are highlighted during a comparison with a reference strain profile acquired by a 5-cm-resolution Rayleigh scatter analyzer under controlled conditions. In comparison with the B-OTDA strain profile, our estimated strain profile has better accuracy, with centimeter spatial resolut ion

Parametric Inversion of Brillouin spectra using L-curve criterion to enhance the accuracy of distributed strain measurement

International audienceTo ensure stability and durability of engineering structure in natural soil, optical fiber sensors have gained interest over last decade. In addition to conventional geophysical sensors, Brillouin spectra based sensor enables to perform distributed strain measurement. Its algorithm performs a strain measurement with a 40cm spatial sampling over several kilometers. The monitoring of engineering installations needs a centimeter spatial sampling and a better strain accuracy. Previous works highlighted that the industrialized algorithm has great limitation for the exploitation of the local information contained into Brillouin spectra. Indeed, based on its asymmetry and broadening, it is possible to estimate local Brillouin frequencies with a better strain accuracy. We propose here to apply a parametric inverse method using L-curve criterion to estimate the strain with a 5cm spatial sampling. To validate this method, a one-to-one scale experiment has been implemented by optical fiber cable at several depths. Comparing the distributed strain provided by the Brillouin based sensor and our algorithm with a reference strain sensor, the proposed algorithm successfully fulfills the combination of a 5cm spatial sampling over kilometers and a high strain accuracy

Validation of a chemiluminescent assay for specific SARS-CoV-2 antibody

Faced with the COVID-19 pandemic and its impact on the availability and quality of both therapeutic and diagnostic methods, the Belgian authorities have decided to launch a procedure for additional evaluation of the performance of serological tests offered for sale on the national territory. This has been proposed with a double aim: (1) an in-depth verification of the analytical and clinical performances presented by the manufacturer and (2) an economy of scale in terms of centralized validation for all the laboratories using the tests subject to evaluation. A retrospective validation study was conducted including the serum of 125 patients in order to determine the analytical and clinical performances of the LIAISON®SARS-CoV-2 from DiaSorin® detecting anti-SARS-CoV-2 IgG and to compare its clinical performance with the enzyme-linked immunosorbent assay (ELISA) test from Euroimmun®, one of the first commercially available tests allowing the detection of anti-SARS-CoV-2 IgA and IgG. The performances of the LIAISON®SARS-CoV-2 satisfied all the acceptance criteria and provided "real world" analytical and clinical performances very close to the ones reported by the manufacturer in its insert kit. Comparison between the LIAISON®SARS-CoV-2 and the ELISA method did not reveal any difference between the two techniques in terms of sensitivities and specificities regarding the determination of the IgG. This study reports the validation of the LIAISON®SARS-CoV-2 allowing to detect IgG antibodies specifically directed against SARS-CoV-2. The analytical and clinical performances are excellent, and the automation of the test offers important rates, ideal for absorbing an extension of testing.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

The Role of Serology for COVID-19 Control:Population, Kinetics and Test Performance Do Matter

SCOPUS: le.jinfo:eu-repo/semantics/publishe

Séparation de sources non négatives parcimonieuses appliquée aux spectres Brillouin acquis par capteur à fibre optique

National audienceStructure Health Monitoring (SHM) is an important issue in EDF. An optical fiber senor enables to acquire distributed strain measurements with a spatial sampling of 40cm over several kilometers. For every sensing point, a Brillouin spectrum is acquired centered on the Brillouin frequency sensitive to temperature and strain into the optical fiber. If the strain is non uniform within the integration base, then the spectrum will be distorted. A method of Non negative Matrix Factorization (NMF) enables to decompose it into several spectral components, centered on local Brillouin frequencies. A method enables to link their amplitudes to their positions within the integration base. Thus, the presented methodology enables to estimate a centimeter strain profile. It is successfully tested on experimental controlled data set. The comparison with a reference measurement enables to validate the presented methodology which permits a better sampling resolution and strain sensitivity.La surveillance d'ouvrage de grande ampleur est une problématique importante au sein d'EDF (Electricité de France). Un capteur à fibre optique permet de mesurer la déformation de manière répartie avec un pas de mesure de 40cm sur plusieurs kilomètres. A chaque distance interrogée, un spectre Brillouin est acquis. Ce spectre est centré sur une fréquence Brillouin sensible à la température et à la déformation imposée par l'ouvrage à la fibre optique. Si la déformation est non uniforme, alors le spectre est distordu. Nous proposons une méthode de Factorisation de Matrices Non négatives (FMN) afin de décomposer le spectre sur une base de spectres Brillouin élémentaires. Un algorithme basé sur leurs amplitudes relatives permet d'estimer la déformation avec une nouvelle résolution spatiale de l'ordre d'un centimètre. Cette méthodologie est testée sur des données expérimentales acquises en milieu contrôlé. La comparaison avec une mesure de référence montre la validité de cette approche

Nonnegative unmixing methodology applied on Brillouin Optical Fiber Sensor

International audienceAs a complement to conventional sensors, Distributed Optical Fiber Sensors (DOFS) have gradually played a prominent role in Structural Health Monitoring (SHM) for the last decade. The distributed Brillouin sensor enables to measure strain along kilometers of cable with a spatial resolution of 1 meter. The challenge is to have a centimeter spatial resolution to improve structure defaults detection and localization. A numerical model, based on the sensor physic, is first proposed in order to study Brillouin spectra distortion depending on strain distribution within spatial resolution. Then, based on nonnegative least squares (NNLS) problem, Brillouin spectra are decomposed into several elementary spectra. The estimated central frequencies and maxima permit to estimate a centimeter frequency distribution within the spatial resolution. It has been verified with numerical and experimental data: that method enables to enhance the accuracy and spatial resolution of the sensor from meter to centimeter

Quantification of sub-millimeter displacements caused by sinkholes, using distributed optical fiber sensors

International audience—The estimation of sinkhole-induced ground displacement is an important issue for monitoring soil structures. Distributed optical fiber sensors composed of an interrogator based on scattering effects in an optical fiber cable sensing element can be used to assess ground displacement. These sensors provide longitudinal strain measurements of the soil structure. This article proposes a methodology that enables estimation of displacement fields in the soil structure when a sinkhole appears. It also exposes an experiment which was carried out to create an artificial sinkhole instrumented by optical fiber sensors. This is the first time that those sensors are used to provide sub-millimeter vertical displacements. The first step of the methodology is to model the ground displacement under two-dimensional conditions. The longitudinal strain measured by a distributed optical fiber sensor can thus be linked to the displacement of the structure. This model is described by those parameters: the spatial extent of the displacement signature; a coefficient that depends on the interface between the optical fiber cable and the soil; the depth of the sinkhole; and the maximal vertical displacement. The second step consists of the estimation of each parameter independently. The spatial extension is given by fitting the measured strain signature with the empirical model. The depth of the sinkhole can be determined by measurement of the spatial extension of the ground-displacement profile at several observation depths in the structure. Finally, the vertical maximal displacement is furnished with high precision

On Lattice QCD with Many Flavors

We discuss the confining and chiral-symmetry breaking properties of QCD with a large number of flavors $N_f$. In a Monte Carlo simulation of QCD with $N_f =16$ staggered fermions, we find clear evidence of a first order bulk phase transition which separates phases with broken and unbroken chiral symmetry. This is consistent with extrapolations of earlier studies with smaller $N_f$, and is also as expected from general arguments. Thus, even when the perturbative renormalization group flow has a new infrared stable fixed point near the origin, lattice artifacts induce chiral symmetry breaking, and presumably confinement, at sufficiently strong coupling.Comment: 10 pages, LaTeX, figures part of the LaTeX fil