Covid-19: Saliva diagnosis emerges as a cheaper, faster method than swab testing

NEW DELHI: A low-cost saliva test that will enable people to collect their own samples with minimal discomfort, without invasive nasal or throat swabs, could well be the way forward to detect the novel coronavirus, say scientists.

Giving a thumbs up to the alternative testing technology that is yet to be introduced in India, scientists said it would deliver results faster and more accurately and also minimise the risk for healthcare workers collecting samples.

The saliva-based Covid-19 diagnosis offers an improvement over standard nasopharyngeal swab methods because people can collect their own samples with ease -- simply spit into a sterile tube and mail it to a lab for processing. "It is also unique because it does not require a separate nucleic acid (RNA) extraction step. This is significant because the extraction kits used for this step in other tests have been prone to shortages in the past," A R Anand, senior associate professor at Chennai's L&T Microbiology Research Centre, told PTI. Noting that the 'saliva direct' test is easier to carry out, he said it needs only a few reagents and a real-time polymerase chain reaction (RT-PCR) machine.


Discussion on the technology intensified after the US Food and Drug Administration (FDA) this week gave the Yale School of Public Health emergency use authorisation for its 'Salivadirect' Covid-19 diagnostic test. The FDA said in a statement that SalivaDirect does not require any special type of swab or collection device. A saliva sample, it said, can be collected in any sterile container.

Though saliva tests are yet to be approved in India for mass use, scientists such as Anand suggest the matter be explored further.

"A fast-tracked study should be conducted in an Indian setting comparing the saliva RT-PCR tests with the nasopharyngeal RT-PCR tests before large-scale implementation in our country," Anand said. An Indian Council of Medical Research (ICMR) scientist added that India is exploring the availability of kits and other aspects. "At present, no kit is approved in India," he said on the condition of anonymity.

According to a recent study published in ICMR's Indian Journal of Medical Research, gargled water samples may be another viable alternative to swabs for detecting Covid-19, enabling easy self-collection and removing the need for trained healthcare workers for sample collection.

Asked about the saliva test cleared by the FDA, ICMR Director General Balram Bhargava on Wednesday told a parliamentary panel that taking samples from gargled water is already under consideration and further details will be available soon.

There are two types of diagnostic tests for Covid-19 testing, both using swabs from the nose and the throat.

The RT-PCR test, which can take hours or even days before a result, detects genetic material of the virus using a lab technique called polymerase chain reaction. The second diagnostic test, the antigen Covid-19 test, detects certain proteins in the virus. An antigen test can also produce results in minutes.

Saliva tests would be an improvement on both.

The collection does not involve material such as swabs -- which can be in short supply -- and the person doing the collection does not need as much training, Satyajit Rath, from New Delhi's National Institute of Immunology, told PTI.

Such systems also reduce the cost since we don't have to depend on one company. Saliva is a much easier sample to collect from patients, compared to nasopharyngeal swabs, which are a little invasive and cause some discomfort to patients, Anand added.

Vineeta Bal, an immunologist from Pune's Indian Institute of Science, Education and Research, said saliva tests might become easily accessible like rapid paper strip tests available for testing blood or urine glucose.

Hence, life can come closer to the 'normal' that we knew of before the pandemic. In India, some researchers are developing the tests for detection from saliva. But as far as I know they are far from reaching the market, Bal added.

Noting the pluses of the Yale saliva test, virologist Shahid Jameel pointed to the ease of sample collection and the reduced cost for extracting RNA, the genetic material of a virus. It would also lead to fewer false negative results.

Most false negative results in the RT-PCR test today are due to improper sampling from the nasopharyngeal area, which is also uncomfortable for the person being tested,Jameel, CEO of the Wellcome Trust/DBT India Alliance, a public charity that invests in building biomedical sciences, told PTI.

In addition to the Yale saliva test, Israel's Center for Geographic Medicine and Tropical Diseases has developed a test that aims to determine in less than a second whether a person is infected with the novel coronavirus.

Noting that the Israel test is yet to be approved, Jameel said it uses the scattering of light by virus particles in mouth washings to estimate both presence or absence, and quantity of virus particles in the sample.

This is based on obtaining data from a large number of positive and negative people and training an algorithm to pick the right scattering patterns. Besides the light source, this test uses artificial intelligence (AI) and machine learning, hoping to get better with time as more samples are analysed, Jameel explained.

Machine learning is an application of AI that provides systems the ability to automatically learn and improve from experience.

Both the tests will reduce time. The Yale test will only cut RNA extraction time as the rest of the process is the same. The Israel test is very quick, Jameel added.

Virologist T Jacob John agreed that the saliva test is a low-cost alternative.

Explaining one of the ways in which saliva test can work, he said, "There is a process of viral genetic material (RNA) converted to DNA, which is then detected by a method different from PCR. It is called '˜loop-mediated isothermal amplification', or LAMP, an original Japanese inventio" John, former head of clinical virology at Christian Medical College, Vellore, told PTI.

LAMP is a cheaper PCR alternative previously used to detect outbreaks of zika and ebola in resource-poor countries.

The final reading is taken by colour reaction -- pink turning to yellow. The equipment is cheaper than PCR equipment. If spit is collected, it avoids the use of special swabs which are in short supply, said John.

Israel and India are conducting trials here on a large sample of patients for four different kinds of technologies, including two Covid-19 tests that could give results in minutes from a saliva sample,according to a statement by the Israeli Embassy in Delhi.