COVID-19 Evidence Alerts
from McMaster PLUSTM

Current best evidence for clinical care (more info)

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Diagnosis Bastos ML, Perlman-Arrow S, Menzies D, et al. 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 Apr;174(4):501-510. doi: 10.7326/M20-6569. Epub 2021 Jan 12.

BACKGROUND: 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.

PRIMARY FUNDING SOURCE: McGill Interdisciplinary Initiative in Infection and Immunity. (PROSPERO: CRD42020203415).

Discipline / Specialty Area Score
Hospital Doctor/Hospitalists
Internal Medicine
Infectious Disease
Occupational and Environmental Health
Family Medicine (FM)/General Practice (GP)
General Internal Medicine-Primary Care(US)
Public Health
Emergency Medicine
Comments from MORE raters

Emergency Medicine rater

Understanding the diagnostic accuracy differences between COVID-19 tests and specimens is important for emergency department clinicians to understand. Some patients arrive refusing NP swabs, while others arrive from the community with COVID test results from outside hospital. In addition, if emergency medicine engages in community surveillance efforts, quantifying the incremental cost increase for detecting one additional SARS-CoV-2 case by NP swab vs saliva collection informs both medical consumers and healthcare provider stewards of the medical dollar.

Emergency Medicine rater

In this meta-analysis, the sensitivity was not statistically different between an NP swab vs saliva. It's also noted the potential cost savings could be huge by using saliva testing. However, several things to note: 1) the cost savings greatly diminished as the prevalence is higher. With prevalence as high as 20-25% currently across certain areas of the country, those cost savings become considerably less; 2) the sensitivity for saliva testing did vary a fair amount based on how the saliva was collected. More data are needed to see what is the optimal collection technique, as well as how well patients can comply with the best technique. Regardless, saliva testing seems to be promising as an alternative and may have the added benefit of allowing pooling of sampling in close circles (eg, families) that could further improve the ability to test larger populations in a more cost-effective manner.

Emergency Medicine rater

Using saliva to detect Covid would be useful.

Internal Medicine rater

A caveat is that we don't really have a "gold" standard, so the sensitivity is likely over-estimated overall.

Public Health rater

This very well developed study provides complementary information for a hot issue, and could help many practitioner and health care manager to inform decision making.