A new preprint study has demonstrated shedding of the SARS-CoV-2 virus in the saliva and feces of patients with Covid-19 suggesting that saliva and feces may be considered as alternative samples to the invasive pharyngeal samples, currently used to diagnose COVID-19. ¹

Researchers from Ghana, Africa undertook a study to determine the presence of SARS CoV-2 in the saliva and feces of confirmed COVID 19-patients who had tested positive by RT PCR test with pharyngeal swabs. The sensitivity and specificity of saliva and fecal samples in detecting the virus was also compared to the routinely collected nasopharyngeal/oropharyngeal swabs.

The study included 50 patients who had confirmed Covid-19 with nasopharyngeal/oropharyngeal samples and 20 suspected COVID-19 patients who had tested negative on pharyngeal samples. The participants were asked to collect the stool (1g) and saliva (early morning;1-2 ml) samples by themselves.

Results showed that out of the 50 Covid-19-positive patients, 50 (86%) also tested positive for SARS-CoV-2 in their saliva samples. An interesting observation was that all 50 fecal samples (100%) of Covid-19 patients tested positive for the virus using the same RT-PCR procedure and test kit.

Compared to the pharyngeal samples, the sensitivity of saliva samples in this study was 86% while the specificity was 100%. This means that RT PCR testing of saliva samples identified 86% of the positive individuals with SARS-CoV 2 as having the COVID-19. The specificity results of 100% suggested that all the participants who tested negative for SARS-CoV 2 using their saliva sample test did not have SARS-CoV 2 when tested with their pharyngeal samples. On the other hand, the fecal samples had a sensitivity and specificity of 100%, which means that all those who tested positive for SARS-CoV 2 using their faecal sample were true positives, and there were no false negatives.

Diagnosis of Covid-19 requires collection and testing of nasopharyngeal or oropharyngeal samples for SARS-CoV-2 collected by trained healthcare workers. Sampling requires the HCWs to be in close proximity to the patient, which puts them at risk of acquiring the infection despite wearing personal protective equipment (PPE) and adhering to all infection control measures.

Moreover, the nasopharyngeal and oropharyngeal sampling methods are invasive methods and cause pain and discomfort to the patient. Patients may cough or sneeze after sampling causing aerosol generation. An injury may occur with incorrect sampling technique. Skull base injury and CSF leak may be a rare complication of nasopharyngeal sample collection.

Therefore, alternative samples such as feces and saliva may not only be beneficial to the patient, in terms of ease of collection and acceptance, but would also greatly limit the risk of exposure of HCWs who are directly involved in the care of Covid-19 patients. It would also reduce the drain of resources, both manpower as well as consumables such as PPE kits, viral transport medium, swab sticks etc. which could be in short supply, particularly in resource-crunched countries.

Reference

1. Badu-Boateng E, et al. A comparative study between nasopharyngeal/oropharyngeal, faecal and saliva viral shedding in Ghanaian COVID-19 patients attending KATH from October-December, 2020. medRxiv, doi: https://doi.org/10.1101/2021.09.04.21262932, September 14, 2021.