Background: A considerable amount of evidence demonstrates the potential of saliva in the diagnosis of COVID-19. Our aim was to determine the sensitivity of saliva versus swabs collected by healthcare workers (HCWs) and patients themselves to assess whether saliva detection can be offered as a cost-effective, risk-free method of SARS-CoV-2 detection.
Methods: This study was conducted in a hospital involving outpatients and hospitalized patients. A total of 3018 outpatients (asymptomatic: 2683, symptomatic: 335) were screened. Of these, 200 qRT-PCR-confirmed SARS-CoV-2-positive patients were recruited (81 asymptomatic, 119 symptomatic). In addition, 101 SARS-CoV-2-positive hospitalized patients with symptoms were also enrolled in the study. From outpatients, HCWs collected nasopharyngeal swabs (NPS), saliva were obtained. From inpatients, HCWs collected swabs, patient-collected swabs, and saliva were obtained. qRT-PCR was performed to detect SARS-CoV-2 by TAQPATH assay to determine the sensitivity of saliva detection. Sensitivity, specificity and positive/negative predictive values (PPV, NPV) of detecting SARS-CoV-2 were calculated using MedCalc.
Results: Of 3018 outpatient swabs tested by qRT-PCR, 200 were positive (males: 140, females: 60; aged 37.85±12.76 years). Of these, saliva was positive in 128 (64%); 39 of 81 asymptomatic (47%),89 of 119 symptomatic patients (74.78%). Sensitivity of detection was 60.9% (55.4-66.3%, CI 95%), with a negative predictive value of 36%(32.9-39.2%, CI 95%).Among 101 hospitalized patients (males:65, females: 36; aged 53.43±15.58 years), with HCW collected NPS as comparator, sensitivity of saliva was 56.1% (47.5-64.5, CI 95%), specificity 63.5%(50.4-75.3, CI95%) with PPV of 77.2% and NPV of 39.6% and that of self-swab was 52.3%(44-60.5%, CI95%), specificity 56.6% (42.3-70.2%, CI95%) with PPV 77.2% and NPV29.7%. Comparison of positivity with the onset of symptoms revealed highest detection in saliva on day 3 after onset of symptoms. Additionally, only saliva was positive in 13 (12.8%) hospitalized patients.
Conclusion: Our results demonstrate the use of saliva to detect SARS-COV-2 in symptomatic patients early after the onset of symptoms. Additionally, these results suggest that saliva may not be recommended as a screening tool at the community level due to the lower detection rate than that for swabs. Saliva testing in symptomatic patients whose nasopharyngeal swab does not detect SARS-CoV-2 reduces false negativity.