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. 2024 Jul 24;8(1):9.
doi: 10.1186/s41512-024-00176-2.

Evaluating diagnostic accuracy of an RT-PCR test for the detection of SARS-CoV-2 in saliva

Natasha Samsunder  1 , Aida Sivro  1   2   3   4 , Razia Hassan-Moosa  1   5 , Lara Lewis  1 , Zahra Kara  1 , Cheryl Baxter  6 , Quarraisha Abdool Karim  1   7 , Salim Abdool Karim  1   7 , Ayesha B M Kharsany  1   2 , Kogieleum Naidoo  1   5 , Sinaye Ngcapu  8   9
Affiliations

Evaluating diagnostic accuracy of an RT-PCR test for the detection of SARS-CoV-2 in saliva

Natasha Samsunder et al. Diagn Progn Res. .

Abstract

Background and objective: Saliva has been proposed as a potential more convenient, cost-effective, and easier sample for diagnosing SARS-CoV-2 infections, but there is limited knowledge of the impact of saliva volumes and stages of infection on its sensitivity and specificity.

Methods: In this study, we assessed the performance of SARS-CoV-2 testing in 171 saliva samples from 52 mostly mildly symptomatic patients (aged 18 to 70 years) with a positive reference standard result at screening. The samples were collected at different volumes (50, 100, 300, and 500 µl of saliva) and at different stages of the disease (at enrollment, day 7, 14, and 28 post SARS-CoV-2 diagnosis). Imperfect nasopharyngeal (NP) swab nucleic acid amplification testing was used as a reference. We used a logistic regression with generalized estimating equations to estimate sensitivity, specificity, PPV, and NPV, accounting for the correlation between repeated observations.

Results: The sensitivity and specificity values were consistent across saliva volumes. The sensitivity of saliva samples ranged from 70.2% (95% CI, 49.3-85.0%) for 100 μl to 81.0% (95% CI, 51.9-94.4%) for 300 μl of saliva collected. The specificity values ranged between 75.8% (95% CI, 55.0-88.9%) for 50 μl and 78.8% (95% CI, 63.2-88.9%) for 100 μl saliva compared to NP swab samples. The overall percentage of positive results in NP swabs and saliva specimens remained comparable throughout the study visits. We observed no significant difference in cycle number values between saliva and NP swab specimens, irrespective of saliva volume tested.

Conclusions: The saliva collection offers a promising approach for population-based testing.

Keywords: COVID-19; Nasopharyngeal swab; SARS-CoV-2; Saliva.

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Conflict of interest statement

The authors declare no competing interests.

Figures

Fig. 1
Fig. 1
Differences in CN values between paired NP swab and saliva SARS-CoV-2 positive samples across different saliva volumes (50 μl, 100 μl, 300 μl, and 500 μl). Paired t-test was used to assess differences in CN values between NP and saliva at specific volumes with no significant differences noted
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