Testing is the cornerstone of the fight against COVID-19, and a test that can be self-administered would greatly increase the options for case identification in the community.
A new study published today in JAMA Internal Medicine, led by Drs. Todd Lee and Emily McDonald from the Research Institute of the McGill University Health Centre (RI-MUHC), confirms the efficiency of saliva testing for COVID-19. This follows a study published earlier this week by another RI-MUHC team showing that saliva samples for COVID-19 testing are as good as nasopharyngeal swabs, but cheaper. These findings could rapidly influence global public health policy for testing strategies.
“Previous studies on the performance of saliva tests showed mixed results, but most of them compared saliva tests to the standard nasal swab test, as if it was a perfect test. Interestingly, there are no perfect tests for COVID-19,” says Dr. Guillaume Butler-Laporte, first author of the study released today.
Using statistical methods for the evaluation of diagnostic tests in the absence of a perfect reference standard, the researchers performed a systematic review of 16 studies comparing the two types of tests (n = 5922 patients). A Bayesian latent class bivariate model was used, developed by Nandini Dendukuri, Associate Professor in the Department of Medicine at McGill University and a scientist at the RI-MUHC. Most studies (15 out of 16) included ambulatory patients, and nine studies exclusively enrolled patients from an outpatient population with mild or no symptoms. The researchers found that the diagnostic accuracy of saliva nucleic acid amplification tests (NAAT) was similar to the nasopharyngeal swab NAAT, especially in the ambulatory setting.
“Saliva tests looked worse than they truly were.”
“The statistical tools and mathematical methods we used provide a more precise estimate of saliva NAAT diagnostic accuracy than the standard meta-analysis methods,” explains Dr. Butler-Laporte, a microbiologist and fellow in infectious diseases, with a background in mathematics and statistics. “Without adjusting for this lack of perfect comparator, it is likely that in previous studies, saliva tests looked worse than they truly were.”
Unlike saliva tests, nasal swab tests require trained healthcare personnel to perform, which limits our testing capacity and our ability to deploy testing programs in the community. In addition, they cannot be easily or reliably performed in all populations, like children and quarantined individuals, note the authors of the study, who argue that it is “incredibly important to validate this [saliva] sampling technique for possible deployment in countries or communities with continually high case rates and especially those with developing healthcare systems and less access to specialized care.”
About the studies
The study Saliva Nucleic Acid Amplification Testing for the Diagnosis of SARS-Cov-2: A Systematic Review and Meta-Analysis, published in JAMA Internal Medicine, was conducted by Guillaume Butler-Laporte, Alexander Lawandi, Ian Schiller, Mandy Yao, Nandini Dendukuri, Emily G. McDonald and Todd C. Lee.
The study The Sensitivity and Costs of Testing for SARS-CoV-2 Infection With Saliva Versus Nasopharyngeal Swabs: A Systematic Review and Meta-Analysis, published in the Annals of Internal Medicine, was conducted by Mayara Lisboa Bastos, Sara Perlman-Arrow, Dick Menzies and Jonathon R. Campbell. It was supported by the McGill Interdisciplinary Initiative in Infection and Immunity (MI4) with seed funding from the MUHC Foundation.
