Temporal profiles of viral load in posterior oropharyngeal saliva samples and serum antibody responses during infection by SARS-CoV-2: an observational cohort study

Abstract

Background Coronavirus disease 2019 (COVID-19) causes severe community and nosocomial outbreaks. Comprehensive data for serial respiratory viral load and serum antibody responses from patients infected with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) are not yet available. Nasopharyngeal and throat swabs are usually obtained for serial viral load monitoring of respiratory infections but gathering these specimens can cause discomfort for patients and put health-care workers at risk. We aimed to ascertain the serial respiratory viral load of SARS-CoV-2 in posterior oropharyngeal (deep throat) saliva samples from patients with COVID-19, and serum antibody responses.Methods We did a cohort study at two hospitals in Hong Kong. We included patients with laboratory-confirmed COVID-19. We obtained samples of blood, urine, posterior oropharyngeal saliva, and rectal swabs. Serial viral load was ascertained by reverse transcriptase quantitative PCR (RT-qPCR). Antibody levels against the SARS-CoV-2 internal nucleoprotein (NP) and surface spike protein receptor binding domain (RBD) were measured using EIA. Whole-genome sequencing was done to identify possible mutations arising during infection.Findings Between Jan 22, 2020, and Feb 12, 2020, 30 patients were screened for inclusion, of whom 23 were included (median age 62 years [range 37-75]). The median viral load in posterior oropharyngeal saliva or other respiratory specimens at presentation was 5·2 log 10 copies per mL (IQR 4·1-7·0). Salivary viral load was highest during the first week after symptom onset and subsequently declined with time (slope -0·15, 95% CI -0·19 to -0·11; R²=0·71). In one patient, viral RNA was detected 25 days after symptom onset. Older age was correlated with higher viral load (Spearman's ρ=0·48, 95% CI 0·074-0·75; p=0·020). For 16 patients with serum samples available 14 days or longer after symptom onset, rates of seropositivity were 94% for anti-NP IgG (n=15), 88% for anti-NP IgM (n=14), 100% for anti-RBD IgG (n=16), and 94% for anti-RBD IgM (n=15). Anti-SARS-CoV-2-NP or anti-SARS-CoV-2-RBD IgG levels correlated with virus neutralisation titre (R²>0·9). No genome mutations were detected on serial samples.Interpretation Posterior oropharyngeal saliva samples are a non-invasive specimen more acceptable to patients and health-care workers. Unlike severe acute respiratory syndrome, patients with COVID-19 had the highest viral load near presentation, which could account for the fast-spreading nature of this epidemic. This finding emphasises the importance of stringent infection control and early use of potent antiviral agents, alone or in combination, for highrisk individuals. Serological assay can complement RT-qPCR for diagnosis.

Clinical and microbiological effect of a combination of hydroxychloroquine and azithromycin in 80 COVID-19 patients with at least a six-day follow up: A pilot observational study

“…The favourable evolution of our patients under hydroxychloroquine and azithromycin paralleled a relatively rapid decrease in viral RNA load as assessed by PCR, which was even more rapid when assessed by culture. These data are important to compare with that of the literature which shows that the viral RNA load can remain high for about three weeks in most patients in the absence of specific treatment [19,23] with extreme cases lasting for more than a month. A study conducted in 76 Chinese COVID-19 inpatients showed that high viral RNA load is associated with the severity of the disease [24].…”

Saliva: potential diagnostic value and transmission of 2019-nCoV

“…Till now, three approaches have been reported to collect salivacoughing out, saliva swabs, and directly from salivary gland duct. In two studies on coughed out saliva, 11 cases out of 12 (91.67%) 11 and 20 cases out of 23 (86.96%) 12 COVID-19 patients were 2019-nCoV RNA positive in saliva, respectively. In one study of saliva swabs, half of 15 (50%) 13 COVID-19 patients were 2019-nCoV RNA positive in saliva.…”

“…Saliva stands at the entry of respiratory system and was also found 2019-nCoV nucleic acid positive. [11][12][13][14] With the nature of noninvasion and less hazard to healthcare workers, saliva specimen collection has the advantages of being more acceptable for patients and more secured for healthcare workers for diagnosis of coronavirus. Till now, three approaches have been reported to collect salivacoughing out, saliva swabs, and directly from salivary gland duct.…”

“…11 Another study from the same group used self-collected saliva from deep throat by COVID-19 patients, tested 2019-nCoV RNA, and analyzed temporal profile of 2019-nCoV load. 12 From this study, saliva mixed with nasopharyngeal and bronchopulmonary secretions from deep throat was collected by coughing out in the morning. 12 Among 23 COVID-19 patients included for this study, 20 cases of their saliva showed detectable 2019-nCoV RNA.…”

French consensus regarding precautions during tracheostomy and post-tracheostomy care in the context of COVID-19 pandemic

“…The duration of contagiousness is still uncertain but is probably more than 25 days [4]. These instructions are therefore valid throughout the management of the tracheotomized patient in the absence of validated data on virus excretion.…”