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Inicio Enfermedades Infecciosas y Microbiología Clínica (English Edition) Usefulness of the Lumiradx™ SARS-COV-2 antigen test in nursing home
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Available online 8 May 2022
Usefulness of the Lumiradx™ SARS-COV-2 antigen test in nursing home
Utilidad del test de antígenos SARS-COV-2 de LumiraDx™ en centros residenciales
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Mercedes Domínguez Fernándeza,
Corresponding author
, Alejandro Seoane Estévezb, Fernando Lamelo Alfonsína, German Boub
a Unidad de Coordinación y Apoyo Asistencial a Residencias Sociosanitarias del Área Sanitaria de A Coruña y Cee, Hospitalización a domicilio, Complejo Hospitalario Universitario A Coruña, A Coruña, Spain
b Servicio de Microbiología, Complejo Hospitalario Universitario de A Coruña, A Coruña, Spain
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Table 1. LumiraDx™ rapid antigen test compared with RT-PCR for the diagnosis of SARS-CoV-2 according to the reason for performing the test.
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The detection of viral ribonucleic acid (RNA) by reverse transcriptase-polymerase chain reaction (RT-PCR) is the reference method for the detection of SARS-CoV-2, but its high price and the overburdening of many laboratories made it necessary to implement techniques that offer fast and reliable results outside the laboratory, such as rapid antigen tests. Their approval for the diagnosis of this infection has meant a change in the strategy against COVID-191 due to their great usefulness in detecting infectious individuals and reducing the spread of the virus1. Their speed and simplicity, as well as it being it possible to perform them at the point of care, have led to them playing an important role in centres outside the hospital environment, such as nursing homes.

The LumiraDx™ SARS-CoV-2 antigen test is a rapid microfluidic immunofluorescence assay that, through the use of test strips, allows direct and qualitative detection of the viral nucleocapsid protein in nasal and nasopharyngeal samples. The usefulness of this technique is based on its high sensitivity and specificity (97.6% and 96.6%, respectively)2. In addition, in symptomatic patients, the concordance with RT-PCR in the first 12 days after the onset of symptoms is 100%. The time to result of this test is about 12min and the result is interpreted by a reading instrument, eliminating the inter-individual interpretation bias of the observer.

The objective of this study was to evaluate the sensitivity and specificity of the LumiraDx™ antigen test in care homes. To do this, a nasal sample was collected from each participant with symptoms compatible with COVID-19 or who were close contacts of patients with COVID-19 in order to perform the LumiraDx™ antigen test (LumiraDx™ Limited, London, United Kingdom) and a nasopharyngeal sample was collected to perform an RT-PCR test, using Allplex™ SARS-CoV-2 reagents (Seegene, Seoul, South Korea). In order to assess whether the negative results obtained using this technique can be used as a criterion when discontinuing isolation, samples were collected from asymptomatic patients already diagnosed with COVID-19 and who had completed the isolation period.

In 46 cases, the antigen test was used for diagnostic purposes. Its sensitivity and specificity were 87.5% and 100%, respectively, with a positive predictive value of 100% and a negative predictive value of 88%. In the symptomatic cases, the sensitivity was 93.33%. In the three cases in which there was discordance (positive RT-PCR and negative antigen), the RT-PCRs showed cycle threshold (Ct) values >33 (Table 1). Previous studies have shown a sensitivity of antigen tests of between 82.2% and 97.6%3–7, figures similar to those reported by the test analysed in this study. In addition, a recent study indicates the LumiraDx™ antigen test to be one of the most sensitive antigen tests3.

Table 1.

LumiraDx™ rapid antigen test compared with RT-PCR for the diagnosis of SARS-CoV-2 according to the reason for performing the test.

    RT-PCRTOTAL
    PositiveNegative
    Symptomatic  Close contact  Symptomatic  Close contact 
LumiraDx™ Ag  Positive  14  21 
  Negative  18  25 
TOTAL15  18  46 

In our study, this test was used in a small sample (24 cases) to assess its usefulness in deciding to end isolation. The sensitivity was 52.63% and the specificity 100%. Both tests coincided in 15 cases: 10 positive and five negative. In the nine cases in which there was disagreement, RT-PCR showed a Ct value >31 after a mean of 16.66 days of infection. Although its sensitivity was low, it should be noted that the antigen test was negative when the RT-PCR showed an elevated Ct value, which, according to the available evidence, would be equivalent to a non-infectious viral load1,8. Therefore, a negative result could support the end of isolation together with compliance with the days of isolation and the absence of symptoms in this vulnerable group, in which access to molecular tests is more difficult.

In short, the LumiraDx™ rapid antigen test has high specificity and good sensitivity in nasal samples from symptomatic and asymptomatic patients. It is an optimal diagnostic tool for SARS-CoV-2 infection and it may be interesting to assess its use in other situations in subsequent studies, such as when deciding to end isolation.

Funding

No funding was received for this study.

Conflicts of interest

The authors declare that they have no conflicts of interest.

References
[1]
Ministerio de Sanidad. Estrategia de detección precoz, vigilancia y control de COVID-19 [accessed 01/04/2021]. Available from: https://www.mscbs.gob.es/profesionales/saludPublica/ccayes/alertasActual/nCov/documentos/COVID19_Estrategia_vigilancia_y_control_e_indicadores.pdf.
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A rapid, high-sensitivity SARS-CoV-2 nucleocapsid immunoassay to aid diagnosis of acute COVID-19 at the point of care: a clinical performance study.
Infect Dis Ther., 24 (2021), pp. 1-9
[3]
N. Kohmer, T. Toptan, C. Pallas, O. Karaca, A. Pfeiffer, S. Westhaus, et al.
The comparative clinical performance of four SARS-CoV-2 rapid antigen tests and their correlation to infectivity in vitro.
J Clin Med., 10 (2021), pp. 328
[4]
L. Porte, P. Legarraga, V. Vollrath, X. Aguilera, J.M. Munita, R. Araos, et al.
Evaluation of a novel antigen-based rapid detection test for the diagnosis of SARS-CoV-2 in respiratory samples.
Int J Infect Dis., 99 (2020), pp. 328-333
[5]
M. Linares, R. Pérez-Tanoira, A. Carrero, J. Romanyk, F. Pérez-García, P. Gómez-Herruz, et al.
Panbio antigen rapid test is reliable to diagnose SARS-CoV-2 infection in the first 7 days after the onset of symptoms.
[6]
M. Domínguez, M.F. Peña, F. Lamelo, G. Bou.
Experiencia con los test rápidos de antígenos PanbioTM para la detección del SARS-CoV-2 en centros residenciales.
Enferm Infecc Microbiol Clin., (2021),
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L. Krüger, J. Klein, F. Tobian, M. Gaeddert, F. Lainati, S. Klemm, et al.
Evaluation of accuracy, exclusivity, limit-of-detection and ease-of-use of LumiraDx™-antigen-detecting point-of-care device for SARS-CoV-2.
[8]
A. Krüttgen, C.G. Cornelissen, M. Dreher, M.W. Hornef, M. Imöhl, M. Kleines.
Comparison of the SARS-CoV-2 rapid antigen test to the real star Sars-CoV-2 RT PCR kit.

Please cite this article as: Domínguez Fernández M, Seoane Estévez A, Lamelo Alfonsín F, Bou G. Utilidad del test de antígenos SARS-COV-2 de LumiraDx™ en centros residenciales. Enferm Infecc Microbiol Clin. 2022. https://doi.org/10.1016/j.eimc.2021.06.006

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