Continuously High Detection Sensitivity of Saliva, Viral Shedding in Salivary Glands and High Viral Load in Patients with COVID-19

Background: Coronavirus Disease 2019 (COVID-19) is wreaking havoc throughout the world. However, we know little about the virus load and changes of laboratory indicators since the infection onset. Pharyngeal swabs are commonly used for COVID-19 diagnosis. However, taking pharyngeal swab is a potential health hazard to health-care workers. It is urgent to find a detection method more protective, sensitive, and time-saving. We aimed to clarify the detection sensitivity of saliva, the viral shedding in salivary glands, the viral load during infection, and change of laboratory tests after symptom onset.Methods: GTEx and TCGA database were used for ACE2 expression analysis. 49 confirmed patients were included from Guangzhou Eighth People’s Hospital. Pharyngeal swabs, oral swabs, rectal swabs, blood and saliva samples were obtained for comparison of virus detection. Saliva was re-collected after patients gargling with 3% hydrogen peroxide (H2O 2) . Viral load was determined by reverse transcription quantitative PCR (RT-qPCR). Changes of laboratory tests was also analyzed.Findings: From January 26 to March 27, a total of 538 specimens were obtained from 49 patients. The SARS-CoV-2 detection rate by positive cases in saliva, oral swabs, pharyngeal swabs, rectal swabs, and blood was 90.2% (37/41), 49.0% (24/49), 83.7% (41/49), 63.6% (14/22) and 17.4% (4/23), respectively. The detection rate by positive times was 83.3% (70/84), 40.5% (30/74), 53.7% (130/242), 52.7% (49/93) and 8.9% (4/45), respectively. And saliva had a higher detection rate than other specimens in each day-ranges after infection onset. The viral load in saliva obtained after gargling with 3% H2O 2 was higher (median 3.581 log10copies/mL) than before (median 3.286 log 10 copies/mL). The viral load was high since symptom onset (median 4.02 log10copies/mL), peaked within 5 days (median 4.27 log10copies/mL), and gradually declined one week after symptom onset. Peak viral load had a positive correlation with age (Spearman r=0.3241, p=0.0231). During infection, leukocytes, neutrophils, regulatory T cells, D-Dimer, C-reactive protein, lactate dehydrogenase, and sodium were significantly increased; while creatinine declined.Interpretation: Saliva is a better specimen for SARS-CoV-2 detection, as it is protective, sensitive, and time-saving. The high expression of ACE2, high detection rate of SARS-CoV-2 RNA in saliva, and continuous viral shedding in salivary glands, all suggest SARS-CoV-2 infection in salivary glands. The viral load peaks within five days since infection onset, indicating that SARS-CoV-2 can be transmitted easily even in mild cases.Funding Statement: This work was supported by the Guangdong Financial Fund for High-Caliber Hospital Construction.Declaration of Interests: The authors declare no conflicts of interest.Ethics Approval Statement: This study was approved by the Ethics Committee of Guangzhou Eighth People’s Hospital.