Saliva samples provide more rapid identification of the SARS-CoV-2 virus than nasal swabs, suggests a new study published today.
“That is important because people can spread COVID-19 before they know that they have it,” says coauthor Donald K. Milton. “Earlier detection can reduce the disease’s spread.”
The study was inspired by the fact that, early in the pandemic, an urgent need to boost testing was coupled by a shortage of supplies, particularly nose swabs, which were then the conventional method for collecting samples for testing.
In May 2020, researchers began testing saliva samples from healthy community volunteers weekly to identify persons with COVID-19, and they continued over the next two years. Milton and his colleagues discovered that asymptomatic participants who tested positive frequently developed symptoms a day or two later.
“That made us wonder whether saliva was better for catching pre-symptomatic patients than the traditional nasal swabs,” he added.
The researchers analyzed data from a companion study of close contacts of persons with confirmed cases of COVID-19 to answer that question.
In the research, “We collected saliva and mid-turbinate [nasal] swab samples from contacts every 2 or 3 days during their quarantine period,” explained Milton. “All 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. We then analyzed how these results changed in the days before and after symptom onset.”
Saliva was significantly more sensitive than mid-turbinate nasal swabs early in the course of infection, particularly before the onset of symptoms, according to the study, which noted that previous studies had shown that pre-symptomatic transmission of SARS-CoV-2 plays a greater role than symptomatic transmission.
The findings have implications for increasing public acceptance of COVID-19 testing, lowering the cost of mass COVID-19 screening, and enhancing the safety of testing healthcare professionals. In the latter situation, saliva self-testing eliminates the close contact between patient and healthcare practitioner associated with nasal swabbing, as well as forcing patients to cough and sneeze, so spreading virus particles and causing 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,” added Milton. “We expect that if rapid saliva tests become available, they could be a major advance from the current nasal swab-based rapid tests.”
Image Credit: Getty