Is saliva collected passively without forceful coughing sensitive to detect SARS-CoV-2 in ambulatory cases? A systematic review

OBJECTIVE: This systematic review was conducted to assess the sensitivity rate of SARS-CoV-2 detection in the saliva of ambulatory asymptomatic and mildly symptomatic patients, with saliva being collected passively without any forceful coughing. STUDY DESIGN: A literature search was performed from January 2020 to July 2021. Prospective studies excluding letters to editors were included in our review only if saliva and nasopharyngeal samples were collected simultaneously and sensitivity was reported using reverse transcription polymerase chain reaction (RT-PCR) in asymptomatic or mildly symptomatic ambulatory cases. RESULTS: A total of 436 studies were assessed; 10 (4 cohorts and 6 cross-sectional) studies met our inclusion criteria. The sensitivity rate of saliva to detect SARS-CoV-2 varied from 85.7% to 98.6% in all except for 3 studies. Lower sensitivity levels were attributed to low viral load (51.9% and 63.8%) or lack of supervision while collecting saliva (66.7%). CONCLUSIONS: Passively collected saliva in the absence of coughing has a high sensitivity rate to detect SARS-CoV-2 in asymptomatic and mildly symptomatic patients compared with nasopharyngeal swabs. Limitations of previous studies, such as lack of attention to the method of saliva collection, stages, and severity of the disease at the time of sample collection, can be researched in future investigations.