A Large Cohort Study of SARS-CoV-2 Detection in Saliva: A Non-Invasive Alternative Diagnostic Test for Patients with Bleeding Disorders

Abstract

Diagnosis of SARS-CoV-2 infections is mostly based on the nasopharyngeal swabs (NPS). However, this collection is invasive and uncomfortable, especially for children and patients with coagulopathies, whose NPS collection often causes bleeding. Thus, the aim of this study was to evaluate the usefulness and accuracy of saliva for the diagnosis of COVID-19 in patients presenting bleeding disorders. Samples of NPS, oropharyngeal swabs (OPS), and saliva were collected simultaneously from 1159 hospitalized patients with hematological diseases and from 524 healthcare workers, both symptomatic and asymptomatic for SARS-CoV-2. All samples were evaluated for SARS-CoV-2 by qRT-PCR. SARS-CoV-2 was detected in NPS, OPS and saliva from 16.9%, 14.4% and 15.6% individuals, respectively. Tests in saliva showed sensitivity, specificity, and overall agreement of 73.3%, 96.9% and 92.7% (=0.74), respectively. Salivary tests had good accuracy (AUC = 0.7) for discriminating negative and positive qRT-PCR for SARS-CoV-2. Higher sensitivity was observed in symptomatic than in non-symptomatic patients, as well as in healthy subjects than in patients with hematological disease, in both OPS and saliva. The mean viral load in NPS was significantly higher than in OPS and in saliva samples (p < 0.001). Saliva is a good diagnostic tool to detect SARS-CoV-2, especially among patients symptomatic for COVID-19, and is a valuable specimen for mass screening of hospitalized patients with hematological diseases, especially for those that with bleeding disorders.

Recent advances in RNA sample preparation techniques for the detection of SARS-CoV-2 in saliva and gargle

“…In several studies, saliva or gargle was diluted with PBS or other types of buffers before RNA extraction. However, dilution of the sample also lowers the concentration of the target RNA [ 6 , 22 , 30 , 36 ]; Lopes et al. [ 6 ] observed that when saliva was 1:1 diluted with viral transport media, clinical sensitivity was decreased (66% vs. 73.3%).…”

“…However, dilution of the sample also lowers the concentration of the target RNA [ 6 , 22 , 30 , 36 ]; Lopes et al. [ 6 ] observed that when saliva was 1:1 diluted with viral transport media, clinical sensitivity was decreased (66% vs. 73.3%). To reduce sample viscosity, several studies treated saliva samples with DTT [ 102 , 103 ], proteinase K [ 104 ], or homogenization [ 105 ].…”

“…[ 27 ] found that the detection rate for SARS-CoV-2 in saliva was higher than in NPS samples (93.1% vs. 52.5%) when testing 217 convalescent patients, suggesting that the viral RNA levels in saliva and NPS are different in convalescent patients. Furthermore, clinical sensitivity of 73.3% was reported when 2/3 samples were collected from inpatients with hematological disease [ 6 ], implying that this disease may influence SARS-CoV-2 distribution in patients.…”

“…Although NPS specimens can be self-collected, the quality of NPS specimens is highly variable and depends on sampling skills. NPS sampling could cause discomfort, coughing and even bleeding in patients with bleeding disorders [ 6 ]. Inadequate sampling of viral components on NPS could cause false negative results [ 7 ].…”

“…[ 25 ] reported similar amounts of viral RNA detected in NPS and saliva from symptomatic patients. Some studies reported that viral load in saliva was higher than in NPS [ 5 , [26] , [27] , [28] ], whereas other studies showed that viral load in saliva was lower than in NPS and that the detection of SARS-CoV-2 in saliva gave higher false negative rates [ 6 , [29] , [30] , [31] ]. These conflicting results could be due to both biological differences and analytical discrepancy.…”