Saliva sample for detection of SARS-CoV-2: A possible alternative for mass testing

Abstract

Molecular diagnostic testing has played a critical role in the global response to the novel Coronavirus disease (COVID-19) pandemic, since its first outbreak in late 2019. At the inception of the COVID-19 pandemic, nasopharyngeal swab sample analysis for COVID-19 diagnosis using the real-time polymerase chain reaction (RT-PCR) technique was the most widely used. However, due to the high cost and difficulty of sample collection, the number of available sample types for COVID-19 diagnosis is rapidly increasing, as is the COVID-19 diagnostic literature. The use of nasal swabs, saliva, and oral fluids as viable sample options for the effective detection of SARS-CoV-2 has been implemented successfully in different settings since 2020. These alternative sample type provides a plethora of advantages including decreasing the high exposure risk to frontline workers, enhancing the chances of home self-sampling, reducing the cost, and significantly increasing testing capacity. This study sought to ascertain the effectiveness of Saliva samples as an alternative for COVID-19 diagnosis in Nigeria. Demographic data, paired samples of Nasopharyngeal Swab and Drooling Saliva were obtained from 309 consenting individuals aged 8-83 years presenting for COVID-19 testing. All samples were simultaneously assayed for the detection of SARS-CoV-2 RdRp, N, and E genes using the GeneFinder™ COVID-19 Plus RT-PCR test kit. Out of 309 participants, only 299 with valid RT-PCR results comprising 159 (53.2%) males and 140 (46.8%) females were analyzed in this study using the R Statistical package. Among the 299 samples analyzed, 39 (13.0%) had SARS-CoV-2 detected in at least one specimen type. Both swabs and saliva were positive in 20 (51.3%) participants. Ten participants (25.6%) had swab positive/saliva-negative results and 9 participants (23.1%) had saliva positive/swab-negative results. The percentage of positive and negative agreement of the saliva samples with the nasopharyngeal swab were 67% and 97% respectively with positive and negative predictive values as 69% and 96% respectively. The findings indicate that drooling saliva samples have good and comparable diagnostic accuracy to the nasopharyngeal swabs with moderate sensitivities and high specificities.

Fig 1

Cycle Threshold (Ct) values for SARS-CoV-2 positivity to (A) E-gene, (B) N-gene, and (C) Orf1ab gene respectively, show good comparison on both the Saliva and the Nasopharyngeal swab: The median Cycle Threshold (Ct) values for the three SARS-CoV-2 genes (E, N, and Orf1ab) of the positive samples (Ct <40) and the negative samples (Ct>40) from both the nasopharyngeal swab and saliva samples were compared using the Wilcon signed rank exact test. The p values of 0.07715, 0.8438, and 0.2293 were determined for the E, N, and Orf1 ab genes respectively. There were no statistically significant differences between the median SARS-CoV-2 E-gene, N-gene, and Orf1ab gene Ct values detected for the Nasopharyngeal swab and Saliva samples.