The Keio Journal of Medicine
Online ISSN : 1880-1293
Print ISSN : 0022-9717
ISSN-L : 0022-9717
RT-PCR Screening Tests for SARS-CoV-2 with Saliva Samples in Asymptomatic People: Strategy to Maintain Social and Economic Activities while Reducing the Risk of Spreading the Virus
Junna ObaHiroaki TaniguchiMasae SatoReika TakamatsuSatoru MorikawaTaneaki NakagawaHiromasa TakaishiHideyuki SayaKoichi MatsuoHiroshi Nishihara
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2021 Volume 70 Issue 2 Pages 35-43


The year 2020 will be remembered for the coronavirus disease 2019 (COVID-19) pandemic, which continues to affect the whole world. Early and accurate identification of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is fundamental to combat the disease. Among the current diagnostic tests, real-time reverse transcriptase–polymerase chain reaction (RT-qPCR) is the most reliable and frequently used method. Herein, we discuss the interpretation of RT-qPCR results relative to viral infectivity. Although nasopharyngeal swab samples are often used for RT-qPCR testing, they require collection by trained medical staff. Saliva samples are emerging as an inexpensive and efficient alternative for large-scale screening. Pooled-sample testing of saliva has been applied for mass screening of SARS-CoV-2 infection. Current policies recommend isolating people with borderline cycle threshold (Ct) values (35<Ct <40), despite these Ct values indicating minimal infection risk. We propose the new concept of a “social cut-off” Ct value and risk stratification based on the correlation of Ct with infectivity. We also describe the experience of RT-qPCR screening of saliva samples at our institution. It is important to implement a scientific approach to minimize viral transmission while allowing economic and social activities to continue.

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© 2021 by The Keio Journal of Medicine
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