Performance of saliva as a specimen to detect SARS-CoV-2

Abstract

Massive testing to detect SARS-CoV-2 is an imperious need in times of epidemic but also presents challenges in terms of its concretization. The use of saliva as an alternative to nasopharyngeal swabs (NPS) has advantages, being more friendly to the patient and not requiring trained health workers, so much needed in other functions. This study used a total of 452 dual samples (saliva and NPS) of patients suspected of having COVID-19 to compare results obtained for the different specimens when using RT-PCR of RNA extracted from NPS and saliva, as well as saliva directly without RNA extraction. SARS-CoV-2 was not detected in 13 saliva (direct) of the 80 positive NPS samples and in 16 saliva (RNA) of a total of 76 NPS positive samples. Sensitivity of detection of viral genes ORF1ab, E and N in saliva is affected differently and detection of these genes in saliva samples presents great variability when NPS samples present Ct-values above approximately 20, with sensitivities ranging from 76.3% to 86.3%. On average an increase in 7.3 Ct-values (average standard deviation of 4.78) is observed in saliva samples when compared to NPS. The use of this specimen should be carefully considered due to the false negative rate and the system used for detection may be also very relevant since the different viral genes are affected differently in terms of detection sensitivity using saliva.

Keywords: COVID-19; False negatives; RT-PCR; SARS-CoV-2; Saliva; Sensitivity.

Fig. 1

Title: Ct values (NPS vs SD). Legend: NPS (red) and differences of NPS to SD (blue) Ct values. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Fig. 2

Title: Ct values (NPS vs SE). Legend: NPS (red) and differences of NPS to SE (blue) Ct values. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)