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

Diagnostic Virology
To KKW et al
Lancet Infect Dis

Main result

On 23 patients, the median viral load in posterior oropharyngeal saliva was 5,2 log10 copies/mL. Salivary viral load was highest during the first week after symptom onset and subsequently declined with time. In one patient, viral RNA was detected 25 days after symptom onset.

Older age was correlated with higher viral load (ρ=0·48 ; p=0·020). For the majority of 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.


The posterior oropharyngeal saliva samples appear to be an interesting alternative to the nasopharyngeal samples. Indeed, the viral load was significant in the saliva of infected patients and those especially during the first week after symptom onset. Viral load is positively correlated with age. 
In plasma serum, seropositivity was found in more than 90% overall for the virus components tested and the higher the level of seropositivity, the lower the viral load. 
In addition, no genetic mutations were found.


Strength of evidence Weak

- Small number of patients and samples
- Study on patients hospitalized in Hong-Kong, therefore more severe patients.


To determine 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


Cohort study at two hospitals in Hong Kong. Included patients had laboratory-confirmed positive COVID-19 test. Blood, urine, posterior oropharyngeal saliva, and rectal swab samples were studied. 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.

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