A Covid-19 testing station in Mangere. Photo / Sylvie Whinray
A Covid-19 testing station in Mangere. Photo / Sylvie Whinray
New research suggesting saliva samples may be more sensitive to detecting Covid-19 than nasal swabs has been met with cautious optimism by New Zealand experts.
The research is from a team led by US-based Kiwi Dr Anne Wyllie and comes after many countries, including New Zealand, were criticised over testing rates for the virus, which has infected 2.7 million and killed almost 200,000 worldwide. Seventeen have died in New Zealand.
Current testing involves taking nasopharyngeal swabs, which can be uncomfortable for the patient and require a health care worker to fully dress in personal protective equipment.
Wyllie and her team, who are all based at the Yale School of Public Health, suggested the use of saliva could allow at-home, self-administered sample collection for accurate large-scale testing. The study was released as a pre-print and has not yet been peer-reviewed.
But scientists in New Zealand were positive about the initial findings.
While not yet peer-reviewed, the study was "very promising", Massey University School of Natural and Computational Sciences senior lecturer Dr Nikki Freed said.
"The authors show that saliva had better sensitivity and was more consistent for detection of the virus than nasopharyngeal swabs.
"From my perspective, saliva has a lot of advantages over nasopharyngeal swabbing, namely that it is easy to self administer and non-invasive. Most people can easily spit in a cup."
The study was one of the first to clearly show the advantages "from the sensitivity and consistency aspect" of using saliva instead of nasopharyngeal swabs, Freed said.
The results of the study indicated saliva performed slightly better than nasopharyngeal swabs at detecting Covid-19, University of Otago in Christchurch dean and head of campus, Professor David Murdoch, said.
The saliva samples were collected by asking patients to repeatedly spit into a sterile urine cup until it was roughly a third full of liquid, he said.
"These findings are important because saliva samples can be obtained relatively easily and can be collected by the patient themselves without the need for swabs."
Wyllie and her team had cautioned that their study only included patients who had moderate or severe disease, and the findings might be different when testing people with mild or asymptomatic disease, Murdoch said.
"They also only collected samples first thing in the morning. So, it will be important to evaluate the performance of saliva samples in people with mild disease and in specimens collected at other times of the day as well in order to gain more confidence in these promising findings."
An alternative Covid-19 testing option would potentially relieve pressure on swab supplies and protect frontline testing staff from potential exposure to the virus, dnature diagnostics & research technical director John Mackay said.
The Yale study indicated the levels of Covid-19 virus were higher in the saliva samples than the transport media the swab was mixed in, but levels of virus were traditionally diluted by mixing the swabs in a relatively large volume of transport media, Mackay said.
"Therefore a comparison of direct testing of swabs vs saliva would be of strong interest … other tests have been validated using saliva - Rutger University - and therefore the use of saliva as an alternative to swabs is of high interest to Covid-19 testing strategies."
Mackay and Freed have both been awarded funding from Crown agency the Health Research Council for Covid-19 related investigations.
Freed will research rapid diagnosis and genome sequencing to follow the coronavirus outbreak. Mackay will research rapid 15-minute diagnostics for distinguishing Covid-19 from flu.
