Saliva Testing for COVID-19 Quicker, Safer than Nasal Swabs

Early in the COVID-19 pandemic, the urgent need to increase testing was accompanied by a shortage of supplies, notably nasal swabs, which were then the standard method for collecting samples for testing. Research conducted in order to come up with a solution to this problem has now found that genetic testing of saliva samples identifies the SARS-CoV-2 virus more quickly than testing of nasal swabs.

To identify people with COVID-19, investigators at the University of Maryland (College Park, MD, USA) began conducting weekly tests of saliva samples from healthy community volunteers in May 2020 and continued over the next two years. Of the asymptomatic volunteers who tested positive, the researchers found that those patients would typically show symptoms a day or two later, making them wonder if saliva was better at catching pre-symptomatic patients than traditional nasal swabs.

To answer that question, the researchers used data from a companion study of close contacts of people with confirmed cases of COVID-19. In the study, the team collected saliva and mid-turbinate nasal swab samples from contacts every two or three days during their quarantine period. All the samples were tested using real-time reverse transcription polymerase chain reaction (RT-PCR) to detect SARS-CoV-2 and measure how much viral RNA was in the samples. The researchers then analyzed how these results changed in the days before and after symptom onset. The findings revealed that early in the course of infection, saliva was significantly more sensitive than mid-turbinate nasal swabs, notably so before the onset of symptoms. The study also noted that previous studies had shown that pre-symptomatic transmission plays a greater role than symptomatic transmission of SARS-CoV-2.

These findings have implications for improving public acceptance of COVID-19 testing, reducing the cost of mass COVID-19 screening and improving the safety of healthcare workers who conduct testing. In the latter case, saliva self-testing avoids the close contact between patient and healthcare worker that nasal swabbing entails and avoids causing patients to cough and sneeze, thereby spreading virus particles as a result of swabbing the sensitive nasal passages, as well as discomfort to patients.

“Our research supports the use of saliva in large-scale screening in schools and workplaces, as a means of improving screening rates, as well as early detection,” said coauthor Donald K. Milton, M.D., DrPH, a professor of occupational and environmental health at the Institute for Applied Environmental Health, University of Maryland School of Public Health, College Park. “We expect that if rapid saliva tests become available, they could be a major advance from the current nasal swab-based rapid tests.”

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