The new guidelines on Covid-19 testing, released by the ICMR on January 10, 2022, depart from the previous advisories which advocated extensive testing. While the previous versions saw large-scale testing for infection as an essential strategy for containment of transmission and regarded testing as a critical pathway for ending the pandemic, the revised guidelines appear to accept the fact that testing alone will not control the pandemic spread.
Over 20 months ago, I had written an op-ed on Covid testing in this paper (bit.ly/3KjZAQD), along with my colleague Surabhi Pandey. As domestic and international critics attacked India’s low testing rates in the early stages of the pandemic, we cautioned that there was no correlation between Covid testing rates and death rates per million population across countries. We argued that “we should continue to implement all the needed public health measures instead of projecting testing rates as the sole path to salvation.” The spotlight on testing remained as the WHO director-general’s slogan of “Test!Test!Test!” was heavily publicised, without picking up the additional public health messages he coupled with this advice. The WHO advisory on masks came much later, though it is now recognised to be the main protection against respiratory virus infection. Even vaccines don’t prevent infection, while they do reduce the severity of illness if infected. In January 2022, it is very clear that the high testing rates in the US and the UK have not prevented high death rates or even high caseloads of infection in those countries.
This does not mean testing is unnecessary. It is needed, but must be judiciously used. The decision to employ a diagnostic test must be driven by the management decisions that flow from it. If the test result does not influence or improve the management, the test kits and the personnel required impose a wasteful use of resources. In the case of Covid testing, the decisions relate to: implications of the result for isolation of an infected person to prevent transmission; decision to institute Covid-specific treatment; decision to discharge of a hospitalised person after treatment and recovery; detection of new variants, with coupled genomic analysis of positive test samples. How does testing meet these objectives, under the new guidelines?
While testing is useful in diagnosing Covid infection, test results vary depending on the timing, nature of test performed, efficiency of sample collection, transport, lab storage and processing. Tests are often negative early after exposure and late during clinical illness, as a rapidly replicating virus is not available for detection. False positive results from RNA fragments from ‘dead viruses’ (detectable till three months in some cases) may incorrectly delay discharge. Rapid antigen tests give more false negative tests than molecular tests. New mutants, like Omicron, are also more difficult to detect with standard tests developed earlier. There is disenchantment with the use of home testing with ‘lateral flow’ tests after the recent surge in the US, while the UK has decided to stop the free supply of home testing kits.
Asymptomatically infected persons, who are seldom tested, are also the vast majority, as we note from the wide gap between the positivity rates of anti-body surveys and viral testing case counts. They do transmit, if they do not wear masks. If everyone scrupulously wears masks, infection is far more effectively prevented than by essentially relying on test results for isolating infected persons. By wearing a proper mask the proper way, asymptomatic, mildly symptomatic, severely symptomatic persons, as well as their contacts, are unlikely to transmit. We now know that many infected persons transmit even before they develop symptoms and go for testing. In such pre-symptomatic persons too, it is the universally mandated mask that is the assured protection against transmission, not the positive test result that comes later.
The new ICMR guidelines do recommend testing for symptomatic persons and also for high-risk contacts of laboratory confirmed cases. Now that several Covid-specific treatments have been identified by clinical trials, a positive test result will help in choosing who and when to treat with what therapy. However, therapy is not needed for mildly ill persons, especially during an Omicron wave. Those with moderate illness may be evaluated for possible anti-viral therapy, while those who are hospitalised will be treated as per their clinical status using drugs, oxygen and mechanical ventilation as may be indicated. Contacts with co-morbidities also may need Covid-specific treatment if they test positive. Individuals travelling abroad too will be tested as per international travel regulations.
For detection of new variants that arrive through international travellers, entry point testing will continue. For variants circulating or newly emerging in the country, samples collected from clinically symptomatic cases and high-risk contacts should suffice. Advisory against mandatory testing of persons undergoing emergency procedures and asymptomatic persons reporting for delivery, surgical or investigational procedures is also welcome, as it mitigates treatment delays and reduces harassment of patients. Exemption of inter-state travellers within the country, from the requirement of getting tested and showing negative test results, is another measure that provides relief to commuters. This reduces inconvenience and eliminates the business of supplying false test certificates.
The author, a cardiologist and epidemiologist, is president, Public Health Foundation of India (PHFI). Views are personal