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Coronavirus | Testing and the importance of low positivity rate

Data source: India COVID-19 Tracker   | Photo Credit: Rijo M. John

Early detection and isolation of potentially infectious individuals are the keys to successfully fighting a viral pandemic. The importance of diagnostic testing to facilitate this cannot be overemphasised. A widely deployed and efficient testing strategy can go a long way in limiting the spread of new cases as it significantly reduces the chance of individuals with undetected virus exposure from roaming freely among unexposed individuals.

Depending on the type of diagnostic test that is used, testing can turn out to be expensive in terms of machinery, manpower, and other resources especially when these resources are at a limited supply. COVID-19 testing required specialised testing kits that were not easily available at the beginning of the pandemic in India in January 2020. Although the World Health Organization (WHO) had declared coronavirus outbreak a Public Health Emergency of International Concern on January 30, 2020 and India had also reported its first case of COVID-19 on the same day, until about the second half of March 2020, India’s COVID-19 testing was largely confined to symptomatic airport travellers and contacts with known sources.

Game of catch-up

India went into a complete nationwide and staggered lockdown starting March 25, 2020. However, our testing strategy for SARS‑CoV‑2 was still being evolved. A closer look at the different revised testing guidelines from the Indian Council of Medical Research (ICMR) throughout the period of the pandemic shows the scope of testing got gradually expanded to include different population subgroups only as new incidences of novel coronavirus infection were reported from those groups. Instead of using it as a pre-emptive strategy, our testing strategy appeared to be a game of catch-up with the spread of the virus. Naturally, the virus always outsmarted this testing strategy.

A complete lockdown is widely perceived as a tool to expand resources including ramping up testing infrastructure along with other healthcare infrastructure instead of being a solution in itself. However, an analysis of the progression of India’s COVID-19 cases and testing reveals that the growth of testing lagged behind that of cases during the pre-peak phase of both the first and the second wave. The second wave saw daily new cases growing three-to-four times higher than the growth of tests.

Vastly underprepared

Although the second wave came more than a year from the onset of the first wave, it appears that India’s testing infrastructure remained highly insufficient and vastly underprepared. This becomes obvious when we see that average daily new cases recorded during the second wave grew more than four-fold compared to that during the peak of the first wave, while the daily average testing grew only by 60% during the same time.

At the end of the first wave of COVID-19, in early February 2021, India was doing about 63 tests per detected case while the daily testing has decreased to 4.5 tests per each detected case during recent times. Even at the peak of the first wave, India was doing about 11.4 tests per detected case. The average daily test positivity rate was only 8.5% at the peak of the first wave, whereas, the average positivity rate reached 22.8% a few days ago when India was reporting close to 400,000 daily new cases. The WHO, on the other hand, recommends raising daily testing enough to bring the test positivity rates below 5% level.

Glaring statistic

Yet another glaring statistic points to the serious deficiency of testing during the current wave of this pandemic. India reported a total of 108 lakhs COVID-19 cases with the help of 20.3 crore tests, during the first wave that lasted about 375 days. However, for the second wave so far, in 95 days, India already reported 130 lakh new cases by conducting only 10.6 crore tests.

At about 229 tests per 1000 people, India’s testing remains below that of 112 other countries. There has been wide variation in testing across states in India too, ranging from a low of only 76 tests per 1,000 people in Nagaland to 1,314 tests per 1,000 people in Lakshadweep. Among the larger states, Madhya Pradesh, West Bengal, Rajasthan, and Uttar Pradesh carried out the lowest number of tests per 1,000 people while Delhi, Jammu & Kashmir, Kerala and Karnataka did the highest.

In recent days, however, several states including Karnataka, Kerala, Andhra Pradesh, Rajasthan, Punjab, Jammu & Kashmir, Himachal Pradesh, Chandigarh and Arunachal Pradesh have been decreasing their daily new tests even as their test positivity rates are still rising. If the tests are reduced while the cases are still rising, it will manifest in an increased test positivity rate. While the reduced number of reported cases may be inadvertently interpreted as a peak of the present wave, the pandemic will continue unabated whether we detect more cases or not. The downside to this would be an unnecessarily prolonged pandemic straining our healthcare system and the economy even further while putting more lives at risk.

Combined capacity

Dr. Balram Bhargava, the chief of ICMR in a press conference on May 11, stated India has a daily capacity of doing 16 lakh RT-PCR tests and 17 lakh Rapid Antigen Tests which indicate a combined capacity of 33 lakh tests per day. Yet, it is unfortunate that India has not done even 20 lakhs of daily testing on any day from the beginning of this pandemic. For a country of 140 crore people, it is grossly inadequate. It is high time India makes use of its full testing capacity and augments this capacity even further to effectively fight this pandemic. The growth of testing should far outpace the growth of the cases in order to be ahead of the epidemic curve rather than chasing it.

(Rijo M. John is Health Economist and Adjunct Professor, Rajagiri College of Social Sciences, Kochi, Kerala.)


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Printable version | Jun 23, 2021 1:11:16 PM | https://www.thehindu.com/sci-tech/science/coronavirus-testing-and-the-importance-of-low-positivity-rate/article34567424.ece

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