Saliva and Nasopharyngeal Swab Testing Show Similar Sensitivity for SARS-CoV-2 Infection Testing
TAKE-HOME MESSAGE
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This systematic review and meta-analysis of 37 studies evaluating 7332 paired samples compared the use of nasopharyngeal swabs versus saliva-based samples for the detection of COVID-19. The authors concluded that the techniques showed similar sensitivity. Assuming a prevalence of 1%, this yielded an incremental cost of $8093 for each COVID-19 infection detected using a nasopharyngeal swab versus a saliva sample.
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This study suggests that saliva-based sampling, which does not require a trained healthcare worker, offers a less-expensive alternative to nasopharyngeal swabs with equivalent sensitivity.
abstract
This abstract is available on the publisher's site.
Access this abstract nowBACKGROUND
Nasopharyngeal swabs are the primary sampling method used for detection of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), but they require a trained health care professional and extensive personal protective equipment.
PURPOSE
To determine the difference in sensitivity for SARS-CoV-2 detection between nasopharyngeal swabs and saliva and estimate the incremental cost per additional SARS-CoV-2 infection detected with nasopharyngeal swabs.
DATA SOURCES
Embase, Medline, medRxiv, and bioRxiv were searched from 1 January to 1 November 2020. Cost inputs were from nationally representative sources in Canada and were converted to 2020 U.S. dollars.
STUDY SELECTION
Studies including at least 5 paired nasopharyngeal swab and saliva samples and reporting diagnostic accuracy for SARS-CoV-2 detection.
DATA EXTRACTION
Data were independently extracted using standardized forms, and study quality was assessed using QUADAS-2 (Quality Assessment of Diagnostic Accuracy Studies 2).
DATA SYNTHESIS
Thirty-seven studies with 7332 paired samples were included. Against a reference standard of a positive result on either sample, the sensitivity of saliva was 3.4 percentage points lower (95% CI, 9.9 percentage points lower to 3.1 percentage points higher) than that of nasopharyngeal swabs. Among persons with previously confirmed SARS-CoV-2 infection, saliva's sensitivity was 1.5 percentage points higher (CI, 7.3 percentage points lower to 10.3 percentage points higher) than that of nasopharyngeal swabs. Among persons without a previous SARS-CoV-2 diagnosis, saliva was 7.9 percentage points less (CI, 14.7 percentage points less to 0.8 percentage point more) sensitive. In this subgroup, if testing 100 000 persons with a SARS-CoV-2 prevalence of 1%, nasopharyngeal swabs would detect 79 more (95% uncertainty interval, 5 fewer to 166 more) persons with SARS-CoV-2 than saliva, but with an incremental cost per additional infection detected of $8093.
LIMITATION
The reference standard was imperfect, and saliva collection procedures varied.
CONCLUSION
Saliva sampling seems to be a similarly sensitive and less costly alternative that could replace nasopharyngeal swabs for collection of clinical samples for SARS-CoV-2 testing.
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Additional Info
Disclosure statements are available on the authors' profiles:
The Sensitivity and Costs of Testing for SARS-CoV-2 Infection With Saliva Versus Nasopharyngeal Swabs: A Systematic Review and Meta-Analysis
Ann. Intern. Med 2021 Jan 12;[EPub Ahead of Print], ML Bastos, S Perlman-Arrow, D Menzies, JR CampbellFrom MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.
Nasopharyngeal swabs are considered the reference standard specimen for SARS-CoV-2 detection, yet they require extensive personal protective equipment and a trained health professional, while being uncomfortable for the patient and relying on specialized supplies. In this study, the authors investigated whether saliva—a less-invasive sample that can be self-collected in a sterile container—was comparable to nasopharyngeal swabs for SARS-CoV-2 detection by pooling 7332 paired samples from 37 studies. The authors found that, overall, the ability to detect SARS-CoV-2 from saliva was not significantly different than from nasopharyngeal swabs, with saliva having 3.4 percentage points lower (95% CI, 9.9 percentage points lower to 3.1 percentage points higher) sensitivity. Importantly, saliva sensitivity did not differ in key subgroups, including individuals without symptoms, outpatients, and persons presenting to assessment centers for testing. This suggests that saliva could replace nasopharyngeal swabs for community-based sampling, freeing precious health professionals for clinical care and ongoing vaccinations. In addition, the authors estimated the difference in cost between nasopharyngeal swabs and saliva. They found that collection of saliva samples over nasopharyngeal swabs would save approximately $636,000 USD per 100,000 persons sampled, while detecting only 79 fewer SARS-CoV-2 infections if 1 in 100 persons sampled were infected. The cost per additional infection detected with nasopharyngeal swabs was $8093 USD—equivalent to the cost of collecting more than 3900 saliva specimens. An important limitation of is that only one included study evaluated children, a group in whom nasopharyngeal swabbing may be difficult. Additionally, no included study evaluated gargle specimens—a “saliva-like” specimen collected by swishing and gargling water or saline that is being used more often. Overall, saliva appears to be similarly sensitive and substantially cheaper than nasopharyngeal swabs while solving many issues nasopharyngeal swabs present.