-Original-

Clinical Feasibility of a Saliva-Based Antigen Qualitative Test for Severe Acute Respiratory Syndrome Coronavirus 2

Nobuyuki Saito^1,2 and Seiji Kosaihira^1,3

¹Division of Infection Control and Prevention, Nippon Medical School Chiba Hokusoh Hospital, Chiba, Japan
²Department of Emergency and Critical Care Medicine, Nippon Medical School Chiba Hokusoh Hospital, Chiba, Japan
³Department of Respiratory Medicine, Nippon Medical School Chiba Hokusoh Hospital, Chiba, Japan

Background: Nasopharyngeal swabs (NPS) are generally used as specimen samples for antigen qualitative tests for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The principle of the reaction to the antigen protein is the same when saliva is used, and saliva samples were reported to be as accurate as NPS for real-time reverse transcription quantitative polymerase chain reaction (RT-qPCR) testing to identify SARS-CoV-2. Unlike NPS collection, self-collected saliva does not expose healthcare workers to the risk of infection. In this study, we evaluated the feasibility of using saliva samples for a SARS-CoV-2 antigen qualitative test (TA2107SA) under development.
Methods: Saliva samples were collected from patients with confirmed or suspected COVID-19 infection and analyzed. The sensitivity, specificity, and concordance index of the antigen qualitative test were calculated using an RT-qPCR test as reference.
Results: Saliva samples were collected from 105 patients. The mean interval from onset to specimen collection was 5.7 days. The mean cycle threshold (Ct) value of RT-qPCR was 31.3. The sensitivity, specificity, and concordance index were 70.7%, 100%, and 0.85, respectively. In 33 patients with Ct values <30, the results of both the RT-qPCR and antigen tests were positive. The sensitivity of the saliva-based TA2107SA SARS-CoV-2 antigen qualitative test was slightly lower than that of the conventional antigen qualitative test using NPS samples from the same patient.
Conclusion: Saliva-based antigen qualitative tests for SARS-CoV-2 are an alternative option during a pandemic.

J Nippon Med Sch 2022; 89: 500-505

Keywords
SARS-CoV-2, COVID-19, rapid antigen test, point of care test, saliva

Correspondence to
Nobuyuki Saito, MD, MPH, PhD, Department of Emergency and Critical Care Medicine, Division of Infection Control and Prevention, Nippon Medical School Chiba Hokusoh Hospital, 1715 Kamagari, Inzai, Chiba 270-1694, Japan
nobu99@nms.ac.jp

Received, December 12, 2021
Accepted, April 13, 2022