Comparison of viral load between saliva and nasopharyngeal swabs for SARS-CoV2: the role of days of symptoms onset on diagnosis

BACKGROUND: Coronavirus disease 2019 (COVID-19) is highly infectious causing millions of deaths worldwide. Nasopharyngeal swabs are the primary sample of choice for the diagnosis of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), thus, to decrease the exposure to potentially infected samples through the collection is a key point to reduce the risk of infection in healthcare workers. OBJECTIVES: This study aimed to evaluate the sensitivity and viral load of saliva specimens by days of symptoms onset comparing to nasopharyngeal swabs in subjects with mild symptoms. METHODS: Saliva and nasopharyngeal swabs samples were collected from São Paulo Hospital workers presenting mild symptoms, such as fever, cough, sore throat, rhinorrhea, myalgia, headaches, anosmia, ageusia, and fatigue. To understand the positivity and viral load, reverse transcription-polymerase chain reaction (RT-PCR) was performed. FINDINGS: Saliva specimens presented a sensitivity of 98.6% compared to nasopharyngeal swabs. Overall, saliva showed lower viral load compared to nasopharyngeal swabs, regarding days of symptoms onset on diagnosis, the first four days had significant changes in viral load and no significant difference was reported in the days five to nine. MAIN CONCLUSIONS: Although RT-PCR of saliva has presented a lower viral load compared to nasopharyngeal swabs, saliva specimens are a potential and reliable candidate for COVID-19 diagnosis through RT-PCR.