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An epidemiologically sound testing strategy

Test tube icon,Medical equipment for testing Covid-19,vector illustration.
EPS 10.

Test tube icon,Medical equipment for testing Covid-19,vector illustration. EPS 10.

On January 10, 2022, the Indian Council of Medical Research released an Advisory on Purposive Testing Strategy for COVID-19 in India . The advisory provides details on ‘Who may be’ and ‘People who need not to be’ tested. It proposes that ‘asymptomatic individuals in community setting’ and ‘contacts of confirmed cases of COVID-19, unless identified as high risk’, amongst others, need not be tested. The latest COVID-19 testing strategy replaces the previous advisory (Version VI), released on September 4, 2020 and inter alia , had the provision of COVID-19 testing on demand for ‘all individuals who wish to get themselves tested’. Clearly, there are a few paradigm shifts in the testing strategy.

Understandably, the revised strategy has now created a flutter and divided epidemiologists and clinicians, pandemic ‘experts’ and television channel commentators, in two halves — of those strongly supporting or vehemently opposing it. So, is the new advisory on COVID-19 testing a right approach? Let us deep dive.

 

Strategies in sync with stages

When the novel coronavirus pandemic began, the virus was new to any setting and every country including India followed a ‘containment strategy’ to stop the virus spread and prevent community transmission. This required aggressive testing to detect every infection and ‘trace and test’ every possible contact of confirmed cases. ‘Test, test and test’ — as it was colloquially referred to — was an approach recommended and followed by all countries across the world. India, following this approach, ramped up COVID-19 testing capacity and two years on, India has set up nearly 3,100 laboratories conducting COVID-19 testing with daily capacity of nearly two million RT-PCR tests. Over the last many months, additional testing approaches and kits such as rapid antigen test (RAT) and home kits for antigen test have been approved.

The aggressive testing approach seems to have worked — to a large extent and till recently. Yet, no country can claim that it has detected every COVID-19 infection. A few high income countries are estimated to have identified one in every two or three infections. In India, based on the fourth round of the COVID-19 national sero survey between June 2021 and July 2021, only one in every 30 infections has been detected. Clearly, an aggressive testing strategy was useful but not enough.

The emergence of Omicron (B.1.1.529) as a variant of concern now has changed the situation drastically. So there is Omicron, with a three- to four-fold higher transmissibility (when compared to the Delta variant) and also a large majority of new infections being asymptomatic. Along with very high new infections in a short period of time, the testing capacity in nearly all countries has been stretched. Countries are revising testing strategies, mostly with the focus on ramping up testing with the use of RATs and home testing kits. The approaches for other public health tools such as contact tracing, isolation and quarantine are also being reviewed and revised.

 

Testing with purpose

Any diagnostic testing — especially in outbreaks, epidemics or pandemics — has two broad objectives: of individual and public health benefits and tracking the extent of infection. At the individual level, early COVID-19 testing can help in a suitable modification in clinical management. However, with a decoupling of ‘infection’ from ‘moderate to severe COVID-19’ and a better understanding of disease epidemiology, it is known that for most asymptomatic or even mild symptomatic individuals (i.e., fully vaccinated, young adults, or those without comorbidities), a confirmatory COVID-19 testing would not alter the treatment. Therefore, testing asymptomatic or majority of mild symptomatic would burden the laboratory capacity with almost no individual benefit in treatment.

Second, the testing of asymptomatic cases would have the public health benefit of reducing transmission (if every infection can be detected at the earliest). However, with Omicron, it is neither feasible for any system nor required as transmission is already widespread and a majority cases are asymptomatic. As the COVID-19 testing capacity has been overwhelmed in even high resource health-care systems, countries are resorting to expanding RATs. However, with the low sensitivity of RAT kits, in a hypothetical scenario of even every infected individual undergoing a COVID-19 test, nearly half of them will be missed. Clearly, at this stage of pandemic, the individual and public health benefits of testing contacts and asymptomatic individuals are very limited, if not zero.

 

Promoting the use of self-purchased RATs has an equity dimension as well. This is in addition to it not being a very effective public health tool. A ramping up of RATs may be useful in a setting where every member of society has equal access by free of cost availability to such kits. However, in India, as per the Government announcement, 800 million Indians are eligible and dependent on free ration during the pandemic; they cannot be expected to purchase testing kits and are not likely to use them. Therefore, promoting RAT kits is unlikely to be a solution in India as well as in many other low and middle income countries.

In public health challenges such as the ongoing COVID-19 pandemic, every health intervention should be deployed to offer the maximum benefits to most citizens. The available laboratory capacity and the testing kits need to be used efficiently, optimally and intelligently. Testing asymptomatic people has a very limited marginal benefit and can overburden an already stretched testing system — which could essentially mean a delay in the COVID-19 test report for those with a high risk of getting moderate to severe disease.

Finally, the argument that testing should be ramped up to get better COVID-19 data is on weak footing. We need to remember that any data collection is a byproduct of public health interventions and not the primary objective. If we can use data being generated currently, even that would be enough to answer most policy questions and guide interventions. Then, in the end, in every country across the world, the final numbers of the pandemic will always be determined by the estimates.

 

A right epidemiological move

The public health tools need to be suitably modified and calibrated at every stage of the pandemic. Two years into the pandemic, there is limited relevance of continuing with the same old strategies for contact tracing, testing and isolation.

India’s pandemic response has received criticism for being guided by clinical experts and being medical care-oriented with excessive attention on hospital beds and intensive care unit facilities and with a focus on care of the sick. The recent advisory on COVID-19 testing is a hint towards a shift toward the public health approach. There appears to be more attention on a pandemic response guided by local epidemiology and the principles of public health. In addition to testing strategy, in the recent weeks, COVID-19 home isolation guidelines and hospital discharge policies have also been revised.

COVID-19 testing has to be used as a public health tool to benefit the most and not as a medical care tool. When the benefit of testing has become limited, as is the case in the current stage, targeted COVID-19 testing — to protect the vulnerable — is the right approach. Public health strategies have to be designed based on local context and cannot and should not be merely ‘copied’ from other settings. There are a few additional things that call for attention. There is a need for developing detailed COVID-19 hospital admission criteria and ensuring a better adherence to COVID-19 treatment guidelines, to prevent unnecessary admission and avoid unproven therapies that are not recommended. To respond to the current surge, there is a need to bring epidemiology and public health approaches to the forefront and ignore the ‘opinion’ of ‘mushrooming experts’ vocal and visible on television and ‘omnipresent’ on social media.

India’s latest advisory on COVID-19 testing is bold, pragmatic and epidemiologically sound. More importantly, it shifts the balance of India’s pandemic response from a ‘treatment oriented’ to a public health focused approach. It is another opportunity to bring science, data, debate, dialogue, evidence, epidemiology and public health in shaping India’s response to the COVID-19 pandemic. The revised COVID-19 testing approach, arguably, is a pandemic strategy in which the rest of the world is likely to follow India.

Dr. Chandrakant Lahariya is a physician-epidemiologist and public policy and health systems specialist. He is the lead co-author of the book, Till We Win: India’s Fight Against The COVID-19 Pandemic


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Printable version | May 22, 2022 10:39:07 pm | https://www.thehindu.com/opinion/lead/an-epidemiologically-sound-testing-strategy/article38268634.ece