Grand Rounds

Saliva vs Nasopharyngeal Swabs for COVID-19 Testing: Do the Costs and Sensitivities Differ?

BACKGROUND AND PURPOSE:

Bastos et al. (Annals of Internal Medicine, 2021) assessed
- The difference in sensitivity for SARS-CoV-2 detection between nasopharyngeal swabs and saliva
- The incremental cost per additional infection detected with nasopharyngeal swabs

Systematic review and meta-analysis
Inclusion criteria
- Studies that included at least 5 paired nasopharyngeal swab and saliva samples
- Studies that reported diagnostic accuracy for SARS-CoV-2 detection
Study design
- Cost inputs were from nationally representative sources in Canada and were converted to 2020 U.S. dollars
Price per test assumptions
- Cost of materials and personnel to collect the samples
- Nasopharyngeal swab collection would take longer, use higher level healthcare personnel, and require more extensive PPE

37 studies | 7332 paired samples
Overall
- Sensitivity of saliva was 3.4 percentage points lower vs nasopharyngeal swabs (95% CI, 9.9 percentage points lower to 3.1 percentage points higher)
- Pooled saliva sensitivity: 86.9% (95% CI, 82.3% to 90.4%)
Among people with previously confirmed SARS-CoV-2 infection
- Sensitivity of saliva was 1.5 percentage points more sensitive vs nasopharyngeal swabs (95% CI, 7.3 percentage points less to 10.3 percentage points more)
Among people without a previous diagnosis
- Sensitivity of saliva was 7.9 percentage points lower vs nasopharyngeal swabs (95% CI, 14.7 percentage points less to 0.8 percentage point more)
Therefore, if one would test 100,000 people without a previous diagnosis in as setting where SARS-CoV-2 had a prevalence of 1%
- Nasopharyngeal swabs would detect 79 more positive cases than saliva but with an incremental cost of $8093 per case detected with nasopharyngeal swabs

COVID-19 PCR tests using saliva appear to have similar sensitivity compared to nasopharyngeal swabs and are also much less expensive

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