Change in Saliva RT-PCR Sensitivity Over the Course of SARS-CoV-2 Infection

Abstract

While real-time reverse transcriptase-polymerase chain reaction (RT-PCR) on nasopharyngeal swabs is the current standard for SARS-CoV-2 detection, saliva is an attractive alternative for diagnosis and screening due to ease of collection and minimal supply requirements. 1,2 Studies on the sensitivity of saliva-based SARS-CoV-2 molecular testing have shown considerable variability. 3 We conducted a prospective, longitudinal study to investigate the testing timeframe that optimizes saliva sensitivity for SARS-CoV-2 detection.

Comparison of Saliva and Mid-Turbinate Swabs for Detection of COVID-19

“…In a study of ambulatory and symptomatic participants whose ages were more evenly distributed, NPS and MTS swabs were highly correlated with a mean of 7 days since onset of symptoms [20]. Congrave-Wilson et al, in agreement with the current study, found that saliva had the highest sensitivity in the first seven days post COVID-19 onset when using NPS as the reference [2]. Becker et al compared the sensitivity of saliva and NPS for detecting COVID-19 in a convalescent cohort 8-56 days since first symptom and found that NPS performed better [21].…”

“…Only one asymptomatic case was identified in our study so we could not compare the sensitivity of the two types of samples among asymptomatic COVID-19 cases. The evidence for using saliva to detect asymptomatic cases was mixed in previous studies [2,10] and further studies are needed to clarify this issue. In conclusion, the use of saliva is preferable for testing pre-symptomatic populations.…”

“…The U.S. Centers for Disease Control and Prevention (CDC) recommend the use of upper respiratory specimens, including but not limited to nasopharyngeal, mid-turbinate nasal, anterior nasal and saliva specimens for the initial diagnosis of COVID-19 [1]. Although nasopharyngeal swabs (NPS) are considered to be the standard for the detection of COVID-19 by most researchers, collection requires the use of trained professionals, can cause discomfort to the patients, and may pose greater risks to healthcare workers during sample collection [1][2][3][4]. Midturbinate swabs (MTS) are sometimes used as an alternative to NPS in an effort to reduce patient discomfort and occupational exposures to healthcare workers [4][5][6].…”

“…Compared to swab-based collection, saliva is even less invasive, more affordable, and can be self-collected with minimal or no supervision [1,7,8]. Existing studies focusing on the sensitivity of NPS compared to MTS, and NPS compared to saliva have produced contradictory results [2,4,[9][10][11]. Few studies directly compare saliva and MTS specimens.…”

“…Previous studies demonstrated that pre-symptomatic transmission results in higher secondary attack rates for both symptomatic and asymptomatic transmission [12,13]. However, most of the existing studies only looked at detection of symptomatic cases after symptom onset [2,4,9,10] and few looked at detection sensitivity starting with the presymptomatic period. Therefore, a study that conducts a direct comparison of MTS and saliva, including an assessment of sensitivity over time (starting during the pre-symptomatic period) is critical to identifying optimally sensitive methods for early detection and effective control of SARS-CoV-2 transmission.…”