Rapid saliva test
On August 15, six and a half months after the first novel coronavirus case was reported in the country, India crossed another grim milestone — 50,000 deaths. The total number of cases reported have reached nearly 2.6 million; India has been reporting the most fresh cases in a day in the world since August 2. This article argues that India should explore the saliva based test soon. Let us see why –
Questions over reporting death tolls –
- More than the total death toll, what is troubling is the shorter time taken for the death toll to double. The toll count crossed 25,000 on July 16 and doubled to over 50,000 in just 30 days.
- It is certain that there is some extent of underreporting of deaths across the country, especially when deaths have occurred outside the health-care system. For instance, reporting of COVID-19 cases and deaths by States such as Gujarat, West Bengal and Telangana have been suspect right from the beginning; the pandemic-defying trend seen in these States is in stark contrast to the rest of the country.
- No combination of factors can explain the low daily mortality figures in Gujarat and Telangana. In fact, in the last one month, the death toll on any single day in Telangana has never crossed 15 and has been in single digits on many days; the State even reported zero deaths on July 26, while in Gujarat, deaths have never crossed 30, except on one day. However, under-reporting notwithstanding, it is unlikely to be huge enough to change the death toll several-fold.
Why death rate is low?
Like in most Southeast Asian countries, deaths per million population have been low in India. While the case fatality rate too has been low, the continuous dip in the rate might be due to more cases, including asymptomatic ones, being detected due to increased testing with rapid antigen tests.
What is the concern now?
- Also, large cities that witnessed strained health-care infrastructure due to the surge in cases, leading to more deaths, seem to have passed the peak.
- A big shortcoming of rapid antigen tests is their low sensitivity, and despite the ICMR’s recommendation, most States have very low rates of validation of negative test results using the molecular method.
- Relying mostly on rapid antigen tests will result in many of the infected continuing to spread the virus.
Saliva based tests –
- The test, called SalivaDirect, has high sensitivity, according to a preprint posted. According to the preprint, SalivaDirect test can detect when the number of virus copies in the saliva sample is as low as six-12 copies per microlitre. In contrast, testing nasopharyngeal swabs leads to false negative test results due to errors at the time of sample collection. The sensitivity was about 93%.
- Collecting and testing saliva samples three steps — collecting saliva without preservative buffers, proteinase K treatment and heat inactivation, and dualplex RT-qPCR virus detection.
Way forward –
- If speed, low cost and constraints of molecular testing capacity are the reasons why many States have embraced rapid antigen testing, the emergency use authorisation granted recently by the U.S’s FDA for a saliva test developed by Yale University should be good news for India.
- This rapid, inexpensive, non-invasive and highly sensitive test that uses saliva samples will not only help detect more cases but also reduce the need for trained care workers to collect samples.
- Collecting nasopharyngeal samples can be uncomfortable to people, discouraging them from getting tested. The saliva test is likely to increase testing compliance.
- The saliva sample can be collected in any sterile container. The diagnostic test also does not require the use of preservatives at sample collection, does not require specialised reagents or equipment for nucleic acid extraction.
- With the testing protocol made freely available, India should facilitate rapid adoption of the tests by States, after local validation. Early results of the saliva test have been encouraging and India will hugely gain by embracing it in lieu of the unreliable rapid antigen test, particularly when the virus spreads to rural areas.
Source – The Hindu
QUESTION – With increasing coronavirus cases in India and subsequent increase in deaths, India should explore the SalivaDirect technique of virus testing. Discuss.