Thursday, 28 March, 2024
HomeCoronavirusSaliva can be more effective than nasopharyngeal swabs for COVID-19 testing

Saliva can be more effective than nasopharyngeal swabs for COVID-19 testing

The addition of a simple processing step to saliva samples before testing may improve COVID-19 detection rate, eliminate the challenges of nasopharyngeal testing, and facilitate mass surveillance, researchers in the United States and Kenya report.

The collection of nasopharyngeal swab (NPS) samples for COVID-19 diagnostic testing poses challenges including exposure risk to healthcare workers and supply chain constraints, according to material published by Elsevier on 10 June 2021.

Saliva samples are easier to collect but can be mixed with mucus or blood, and some studies have found that they produce less accurate results.

A team of researchers has found that an innovative protocol that processes saliva samples with a bead mill homogeniser before real-time PCR (RT-PCR) testing results in higher sensitivity compared with NPS samples. Their protocol appears in The Journal of Molecular Diagnostics, published by Elsevier.

"Saliva as a sample type for COVID-19 testing was a game changer in our fight against the pandemic. It helped us with increased compliance from the population for testing along with decreased exposure risk to the healthcare workers during the collection process," said lead investigator Dr Ravindra Kolhe of the Department of Pathology in the Medical College of Georgia at Augusta University in George, US.

The study included samples from a hospital and nursing home as well as from a drive-through testing site. In the first phase (protocol U), 240 matched NPS and saliva sample pairs were tested prospectively for SARS-CoV-2 RNA by RT-PCR.

In the second phase of the study (SalivaAll), 189 matched pairs, including 85 that had been previously evaluated with protocol U, were processed in an Omni bead mill homogeniser before RT-PCR testing. An additional study was conducted with samples with both protocol U and SalivaAll to determine if bead homogenisation would affect the clinical sensitivity in NPS samples. Finally, a five-sample pooling strategy was evaluated.

Twenty positive pools containing one positive and four negative samples were processed with the Omni bead homogeniser before pooling for SARS-CoV-2 RT-PCR testing and compared to controls.

In Phase I, 28.3% of samples tested positive for SARS-CoV-2 from either NPS, saliva, or both. The detection rate was lower in saliva compared to NPS (50.0% vs. 89.7%). In Phase II, 50.2% of samples tested positive for SARS-CoV-2 from either saliva, NPS, or both.

The detection rate was higher in saliva compared to NPS samples (97.8% vs. 78.9%). Of the 85 saliva samples tested with both protocols, the detection rate was 100% for samples tested with SalivaAll and 36.7% with protocol U.

Kolhe observed that the underlying issues associated with lower sensitivity of saliva to RT-PCR testing could be attributed to the gel-like consistency of saliva samples, which made it difficult to accurately pipet samples into extraction plates for nucleic acid extraction. Adding the homogenisation step rendered the saliva samples to uniform viscosity and consistency, making it easier to pipet for the downstream assay.

He and his colleagues also successfully validated saliva samples in the five-sample pooling strategy. The pooled testing results demonstrated a positive agreement of 95%, and the negative agreement was found to be 100%.

Pooled testing will be critical for SARS-CoV-2 mass surveillance as schools reopen, travel and tourism resume, and people return to offices.

"Monitoring SARS-CoV-2 will remain a public health need," Kolhe said. "The use of a non-invasive collection method and easily accessible sample such as saliva will enhance screening and surveillance activities and bypass the need for sterile swabs, expensive transport media, and exposure risk, and even the need for skilled healthcare workers for sample collection."

 

Study details

Clinical Validation of a Sensitive Test for Saliva Collected in Healthcare and Community Settings with Pooling Utility for Severe Acute Respiratory Syndrome Coronavirus 2 Mass Surveillance

Nikhil S Sahajpal, Ashis K Mondal, Sudha Ananth, Allan Njau, Pankaj Ahluwalia, Vamsi Kota, Kevin Caspary, Ted M Ross, Michael Farrell, Michael P Shannon, Sadanand Fulzele, Alka Chaubey, Madhuri Hegde, Amyn M Rojiani and Ravindra Kolhe.

Author affiliations: Augusta University in Georgia, United States; Global Laboratory Services in Massachusetts; Georgia Institute of Technology, Georgia Army National Guard and Aga Khan University Hospital in Kenya.

Published in Journal of Medical Diagnostics July 2021: Volume 23, Issue 7.

 

Introduction

The clinical performance of saliva compared with nasopharyngeal swabs (NPSs) has shown conflicting results in healthcare and community settings. In the present study, a total of 429 matched NPS and saliva sample pairs, collected in either healthcare or community setting, were evaluated.

Phase-1 (protocol U) tested 240 matched NPS and saliva sample pairs; phase 2 (SalivaAll protocol) tested 189 matched NPS and saliva sample pairs, with an additional sample homogenization step before RNA extraction.

A total of 85 saliva samples were evaluated with both protocols. In phase-1, 28.3% (68/240) samples tested positive for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) from saliva, NPS, or both. The detection rate from saliva was lower compared with that from NPS samples (50.0% versus 89.7%).

In phase-2, 50.2% (95/189) samples tested positive for SARS-CoV-2 from saliva, NPS, or both. The detection rate from saliva was higher compared with that from NPS samples (97.8% versus 78.9%).

Of the 85 saliva samples evaluated with both protocols, the detection rate was 100% for samples tested with SalivaAll, and 36.7% with protocol U. The limit of detection with SalivaAll protocol was 20 to 60 copies/mL. The pooled testing approach demonstrated a 95% positive and 100% negative percentage agreement.

This protocol for saliva samples results in higher sensitivity compared with NPS samples and breaks the barrier to using pooled saliva for SARS-CoV-2 testing.

 

Science Daily story – Saliva can be more effective than nasopharyngeal swabs for COVID-19 testing, researchers find (Open access)

Journal of Medical Diagnostics article – Clinical Validation of a Sensitive Test for Saliva Collected in Healthcare and Community Settings with Pooling Utility for Severe Acute Respiratory Syndrome Coronavirus 2 Mass Surveillance (Open access)

 

SEE ALSO FROM THE MEDICALBRIEF ARCHIVES

 

A new gold standard? Sputum testing provides higher rate of COVID-19 detection

Detection efficacy of self-collected saliva and deep nasal swabs — large US study

Saliva-based COVID-19 diagnostic test given FDA emergency use authorisation

UK statisticians: 'Spiking' of COVID-19 saliva tests is distorting claimed accuracy

 

 

MedicalBrief — our free weekly e-newsletter

We'd appreciate as much information as possible, however only an email address is required.