Clinical evaluation of self-collected saliva by RT-qPCR, direct RT-qPCR, RT-LAMP, and a rapid antigen test to diagnose COVID-19

  1. Mayu Ikeda
  2. Kazuo Imai
  3. Sakiko Tabata
  4. Kazuyasu Miyoshi
  5. Nami Murahara
  6. Tsukasa Mizuno
  7. Midori Horiuchi
  8. Kento Kato
  9. Yoshitaka Imoto
  10. Maki Iwata
  11. Satoshi Mimura
  12. Toshimitsu Ito
  13. Kaku Tamura
  14. Yasuyuki Kato
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Abstract

Background

The clinical performance of six molecular diagnostic tests and a rapid antigen test for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) were clinically evaluated for the diagnosis of coronavirus disease 2019 (COVID-19) in self-collected saliva.

Methods

Saliva samples from 103 patients with laboratory-confirmed COVID-19 (15 asymptomatic and 88 symptomatic) were collected on the day of hospital admission. SARS-CoV-2 RNA in saliva was detected using a quantitative reverse-transcription polymerase chain reaction (RT-qPCR) laboratory-developed tes (LDT), a cobas SARS-CoV-2 high-throughput system, three direct RT-qPCR kits, and reverse-transcription loop mediated isothermal amplification (RT-LAMP). Viral antigen was detected by a rapid antigen immunochromatographic assay.

Results

Of the 103 samples, viral RNA was detected in 50.5–81.6% of the specimens by molecular diagnostic tests and an antigen was detected in 11.7% of the specimens by the rapid antigen test. Viral RNA was detected at a significantly higher percentage (65.6–93.4%) in specimens collected within 9 d of symptom onset compared to that of specimens collected after at least 10 d of symptom onset (22.2–66.7%) and that of asymptomatic patients (40.0–66.7%). Viral RNA was more frequently detected in saliva from males than females.

Conclusions

Self-collected saliva is an alternative specimen diagnosing COVID-19. LDT RT-qPCR, cobas SARS-CoV-2 high-throughput system, direct RT-qPCR except for one commercial kit, and RT-LAMP showed sufficient sensitivity in clinical use to be selectively used according to clinical settings and facilities. The rapid antigen test alone is not recommended for initial COVID-19 diagnosis because of its low sensitivity.

Key points

Six molecular diagnostic tests showed equivalent and sufficient sensitivity in clinical use in diagnosing COVID-19 in self-collected saliva samples. However, a rapid SARS-CoV-2 antigen test alone is not recommended for use without further study.

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