SARS-CoV-2 saliva testing using RT-PCR: a systematic review

OBJECTIVES: There remain challenges in using SARS-CoV-2 RNA diagnostic assays in the respiratory tract in a pandemic. More so certain countries such as Hong Kong have already included saliva as part of their mass-testing protocol. The aim of this study was to conduct a systematic review on the alternate use of saliva as a SARS-CoV-2 RNA testing specimen in the context of mass screening with reverse transcription polymerase chain reaction. METHODS: Our search methodology was modeled after the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) checklist, and the risk of bias of the selected studies was qualitatively assessed. The percentage individual positive and percentage agreement of both index (saliva) and reference (nasopharyngeal swab), in preference to specificity and sensitivity, were estimated using Kappa statistics. RESULTS: A total of 44 studies met the inclusion criteria. The average percentage positive saliva cases was 72.7% (95% confidence interval), which was lower but not substantially different from the percentage positive NPS of 78.7% (95% confidence interval), and there was an average overall agreement of 89.7% (95% confidence interval). CONCLUSION: Although the literature supports nasopharyngeal swab as a superior testing specimen, an alternative clinical specimen in saliva may offer potential benefits such that a potentially reduced accuracy may be tolerated, especially in low socioeconomic regions.