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Comparative Study
. 2021 Jul 5;21(1):648.
doi: 10.1186/s12879-021-06343-w.

Comparison of saliva with healthcare workers- and patient-collected swabs in the diagnosis of COVID-19 in a large cohort

Mitnala Sasikala  1 , Yelamanchili Sadhana  2 , Ketavarapu Vijayasarathy  3 , Anand Gupta  4 , Sarala Kumari Daram  4 , Naveen Chander Reddy Podduturi  4 , Duvvur Nageshwar Reddy  5
Affiliations
Comparative Study

Comparison of saliva with healthcare workers- and patient-collected swabs in the diagnosis of COVID-19 in a large cohort

Mitnala Sasikala et al. BMC Infect Dis. .

Abstract

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 were tested. Of these, 200 qRT-PCR-confirmed SARS-CoV-2-positive patients were recruited for further study. 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 outpatients (asymptomatic: 2683, symptomatic: 335) tested by qRT-PCR, 200 were positive (males: 140, females: 60; aged 37.9 ± 12.8 years; (81 asymptomatic, 119 symptomatic). Of these, saliva was positive in 128 (64%); 39 of 81 asymptomatic (47%),89 of 119 symptomatic patients (74.8%). 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 53.48 ± 15.6 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: Saliva which is easier to collect than nasopharyngeal swab is a viable alternate to detect SARS-COV-2 in symptomatic patients in the early stage of onset of symptoms. Although saliva is currently not recommended for screening asymptomatic patients, optimization of collection and uniform timing of sampling might improve the sensitivity enabling its use as a screening tool at community level.

Keywords: Healthcare worker; Nasopharyngeal swab; SARS-COV-2; Saliva.

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Conflict of interest statement

The authors declare that they have no competing interests.

Figures

Fig. 1
Fig. 1
Flow of participants in the study
Fig. 2
Fig. 2
Comparison of Nasopharyngeal swab with saliva. Nasopharyngeal swabs and saliva were tested in outpatients: Left panel shows overall positivity of swabs to be higher in comparison to saliva. Middle panel shows comparison of saliva in swab positive patients with higher detection in swabs.Right panel shows higher positivity in symptomatic patients in comparison to asymptomatic patients
Fig. 3
Fig. 3
Comparison of nasopharyngeal swabs collected by healthcare workers (HCWs) and self-swabs vs saliva. The left panel shows positivity in all three specimens, and the right panel shows higher detection rates in saliva between 3 and 5 days of onset of symptoms
Fig. 4
Fig. 4
Matched patients swab and saliva viral genes. Scatter plots of Ct values of ORF, N and S genes in patients whose swab and saliva were positive. Panel A; Ct values of the three genes in all the patients, Panel B; Ct values of three genes in asymptomatic patients, Panel C; Ct values of three genes in symptomatic patients. X axis represents Ct values of N, ORF, S genes and Y axis represents the number of patients. Ct values of the 3 genes did not show any significant difference in asymptomatic patients, while in symptomatic patients, Ct values of the ORF (p = 0.002) and S (p = 0.0007) genes were significantly lower in swabs than saliva samples, while the N gene had no significant difference
See this image and copyright information in PMC

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