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Low sensitivity of rapid antigenic tests as a screening method in an outbreak of SARS-CoV-2 infection in prison
Baja sensibilidad de los test rápidos antigénicos como método de cribado en un brote de infección por SARS-CoV-2 en prisión
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Andrés Marcoa,b,
Corresponding author
amarco@gencat.cat

Corresponding author.
, Concepció Soléc, Indiana J. Abdoc, Elisabet Turua
a Programa de Salud Penitenciaria, Instituto Catalán de la Salud, Barcelona, Spain
b CIBER Epidemiologia y Salud Pública (CIBERESP), Madrid, Spain
c Equipo de Atención Primaria Penitenciaria, Figueres, Girona, Spain
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Dear Editor,

At present, the gold standard for the diagnosis of SARS-CoV-2 infection is detection of viral RNA by means of real-time polymerase chain reaction (rt-PCR) testing or an equivalent molecular technique. In Spain, rapid antigen testing (RAT) that is duly validated (sensitivity ≥80% and specificity ≥97%) can be used within five days of the onset of symptoms in patients with no major immunosuppression and no criteria for intensive care unit (ICU) admission1. RAT is less sensitive than rt-PCR testing in all stages of the infection, and even less so in asymptomatic cases, but its use in the absence of symptoms has not been ruled out in all cases1–3. A recent report from the European Centre for Disease Prevention and Control (ECDC) recommends the use of RAT in patients with or without symptoms if a rate of positive tests ≥10% is anticipated2. It also advises its use in high-risk settings to quickly identify infected individuals and implement prevention and control measures to curb transmission, though it does recommend that negative cases be confirmed with rt-PCR testing1–3.

We report the results of the use of RAT in a SARS-CoV-2 outbreak that occurred on a residential unit (RU) of Figueras prison in Girona, Spain, in late 2020. Between 23 and 25 December, SARS-CoV-2 infection was diagnosed by RAT (Panbio™ COVID-19 Ag tests, Abbott) in three inmates with mild respiratory symptoms. The RU was isolated, and on the afternoon of 25 December the rest of the population was screened with RAT (n = 81). Nine inmates (11.1%) tested positive. They were separated from the others, isolation measures were kept in place and the RU was considered a low-complexity COVID unit given the number of asymptomatic and mildly symptomatic cases with no criteria for hospital admission. The unit was equipped with organisational and functional resources to ensure care safety, quality and efficiency. Cleaning, laundry, waste management and distribution of food and medication was organised according to the recommendations of the Catalan Health Department4. The following were indicated: a) strict isolation of the unit with essential healthcare and non-healthcare personnel entering and exiting; b) mandatory use of personal protective equipment (PPE); and c) clinical examinations (oxygen saturation, temperature and questions about the possible onset of symptoms) twice daily.

On 28 December, rt-PCR testing was performed in the 72 cases with previously negative RAT, yielding positive results in 27 (37.5%) of them (Fig. 1). All followed a good clinical course and there were no hospital admissions.

Fig. 1.

Screening and results obtained in the outbreak on the residential unit in Figueras prison.

(0.23MB).

The prevalence of infection (46.4%) was high as the outbreak occurred in an enclosed space. In situations of confinement, it is estimated that the contagion rate (R0: mean number of people infected by an infected person) may be five to 14 times higher than usual (normally, 1.5–3.0)5; this explains the high number of infections detected in the outbreak. The measures adopted were satisfactory and rt-PCR testing results were negative in all contacts at seven and 14 days.

Regarding the use of RAT in asymptomatic close contacts, some studies (an original6, a letter to the editor7 and several preprints8–10) have shown it to have a specificity equal or close to 100%7–10, but a much lower sensitivity, between 33% and 66%6–10. None of these studies was conducted in contacts from an outbreak or in confined groups. In the cases on the RU, the sensitivity was 25% and the negative predictive value, a key indicator in scenarios in which the prevalence can be considered moderate or high, was 63%. Although RAT is appealing as it is a quick and easy technique that does not require qualified operators, the risk of false negatives is high, even in an outbreak in a confined space with a high prevalence of positive results such as the one reported. Consequently, rt-PCR testing should be the test of choice in screening asymptomatic patients. Only if rt-PCR test results cannot be obtained quickly and there is a high risk of transmission could initial screening with RAT be advisable. In those cases, negative results should be confirmed with subsequent rt-PCR testing, as can be deduced from this study and as is suggested by the guidelines and protocols from the Spanish Ministry of Health1, the ECDC2 and the United States Centers for Disease Control and Prevention (CDC)3.

Funding

The authors declare that they received no funding to conduct this study.

References
[1]
Estrategia de detección precoz, vigilancia y control de COVID-19. Centro de Coordinación de Alertas y Emergencias Sanitarias. Ministerio de Sanidad. Actualizado a 18 de diciembre de 2020 [accessed 2 Jan 2021]. Available from: https://www.mscbs.gob.es/profesionales/saludPublica/ccayes/alertasActual/nCov/documentos/COVID19_Estrategia_vigilancia_y_control_e_indicadores.
[2]
European Centre for Disease Prevention and Control: Options for the use of rapid antigen tests for COVID-19 in the EU/EEA and the UK; 19 November 2020 [accessed 3 Jan 2021]. Available from: https://www.ecdc.europa.eu/en/publications-data/options-use-rapid-antigen-tests-covid-19-eueea-and-uk.
[3]
Centers for Disease Control and Prevention (CDC). Interim Guidance for Antigen Testing for SARS-CoV-2. Update Dec. 16, 2020 [accessed 4 Jan 2021]. Available from: Interim Guidance for Antigen Testing for SARS-CoV-2 | CDC.
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Servei Català de la Salut. Guia d’actuació enfront de casos d’infecció pel nou coronavirus SARS-CoV-2 a les residencies [accessed 3 Jan 2021]. Available from: https://canalsalut.gencat.cat/web/.content/_A-Z/C/coronavirus-2019-ncov/material-divulgatiu/guia-actuacio-residencies.pdf.
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L. Dietz, P.F. Horve, D.A. Coil, M. Fretz, J.A. Eisen, K. Van den Wymelenberg.
2019 novel coronavirus (COVID-19) pandemic: built environment considerations to reduce transmission.
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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.
[7]
F. Fenollar, A. Bouam, M. Ballouche, L. Fuster, E. Prudent, P. Colson, et al.
Evaluation of the Panbio Covid-19 rapid antigen detection test device for the screening of 2 patients with Covid-19.
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M. Masiá, M. Fernández-González, M. Sánchez, M. Carvajal, J.A. García, N. Gonzalo, et al.
Nasopharyngeal Panbio COVID-19 antigen performed at point-of-care has a high sensitivity in symptomatic and asymptomatic patients with higher risk for transmission and older age.
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I. Torres, S. Poujois, E. Albert, J. Colomina, D. Navarro.
Real-life evaluation of a rapid antigen test (Panbio™ COVID-19 Ag Rapid Test Device) for SARS-CoV-2 detection in asymptomatic close contacts of COVID-19 patients.
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Evaluation of the Panbio™ rapid antigen test for SARS-CoV-2 in primary health care centers and test sites.

Please cite this article as: Marco A, Solé C, Abdo IJ, Turu E. Baja sensibilidad de los test rápidos antigénicos como método de cribado en un brote de infección por SARS-CoV-2 en prisión. Enferm Infecc Microbiol Clin. 2022;40:152–154.

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