Data | Why is it necessary to test more to reduce the impact of COVID-19?

Among countries with the highest case load, India's tests per case has reduced slightly, which means it conducts fewer tests to detect a case as infections have increased

A medic collects samples of a pregnant woman for COVID-19 testing at a kiosk outside Chitaguppi hospital in Hubballi on Thursday. PTI

Nearly 6 million people have been infected by COVID-19 resulting in more than 3.65 lakh deaths across the world. Most countries have implemented lockdowns for physical distancing to arrest the spread of the virus, but data collected over three months of the pandemic show that early testing, isolation and treatment is the surest way of reducing the impact of the pandemic irrespective of the stringency of the lockdown. How does India fare in comparison with other countries and how do Indian States stack up on the testing front?

In proportion

While India ranks among the top-10 countries in the number of confirmed COVID-19 cases, the infections as a proportion of its population are much lower compared to countries with the most cases. However, testing rates in India are also very low, ruling out any reason for relief. The chart compares the number of tests conducted per million of a country's population with the number of cases per million (as on Friday, May 29). The size of the circle corresponds to the total number of cases.

Story of case and testing

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A steady rise

Even though, India had fewer infections than many countries in March and April, cases have steadily risen every day to pitchfork the country as among the top 10 countries with most number of cases. With more than 1.75 lakh cases, India's case trajectory has also been on a slow up-swing unlike U.S. and countries in Europe, where the case increase has slowed down distinctly. See Chart below for the steady rise in cases in India compared to other countries with more than 1,00,000 cases.

Where India stands

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Testing impact

One way to determine whether the lockdown had an impact on arresting the case rise to check the "doubling time"* for each country. The chart plots the stringency index^ for each country against total tests conducted per 1,000 people. Countries with doubling time greater than 35 days are marked in Green, between 15 and 35 days in Orange, and below 15 days in Red. Size of the circles correspond to the total number of cases.

Stringency and doubling time

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Testing more

In terms of total number of tests, India ranks third world-wide. More than 1,00,000 tests were conducted in the last seven days. Only the U.S. (3.7 lakh tests) and Russia (2.66 lakh) have conducted more tests overall in the last week. Clearly India has been ramping up its test rate in overall terms.

Seven-day rolling average of new tests conducted for countries with more than 1 lakh cases

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Test ratios

But in terms of tests per 1,000 people - a better way to find out what is the proportion of people who are being tested, India ranks relatively low among countries with the most cases. This is understandable, considering India's high population compared to these countries.

Tests conducted per 1,000 people

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Test strategy

Tests conducted for each identified case is a better metric to find out how India compares globally. Among countries with the highest case load, India's tests per case has reduced slightly, which means it conducts fewer tests to detect a case as infections have increased.

Tests conducted per confirmed case

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Average tests in States

This graph looks as the rollng average number of tests conducted (every seven days) since April 1. Interestingly Kerala, which had reduced its case load significantly has conducted the fewest tests on an average among major States.

Seven-day rolling average of new tests conducted in Indian States with at least 1,000 cases

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Tests per million

However, when testing rate is considered with respect to population, Kerala had a high test rate initially, which had slowed down over time. Testing at a high rate early helped the State reduce its case load significantly, before the influx of migrants from abroad and other States.

Tests conducted per million people

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Tests per cases

Kerala's relatively better performance is highlighted in this graph that compares tests per case over time. Maharashtra, Gujarat, Delhi and M.P. fare among the worse off States in this metric with relatively higher cases and lower tests per confirmed case.

Tests conducted per confirmed case

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Tests per case worldwide

Countries affected by the virus are divided into two groups (lower - marked in green, and higher case loads - marked in red). Evidently most countries that have tested more over time have reduced their case loads significantly compared to those that have not tested enough.

Effects of early testing

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Stringency impact

Despite having among the most stringent lockdowns, cases in India have continued to rise steadily and fast. Clearly, the lockdown has not had as major an impact as high testing rates have, for other countries that have managed to flatten the infection curves.

Stringency index vs. total cases for countries with more than one lakh cases

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Last word

A high test rate for COVID19 has emerged as the sureshot way of reducing the impact of the pandemic across the world. Lockdowns have helped in physical distancing, but a sure way of limiting the growth of the infection spread has been to test significantly, isolate infected patients and treat them. Within India, States like Kerala had tested at a high rate relative to its population initially (despite following the same ICMR guidelines as a protocol for identifying test cases). Kerala managed to do so by maximising contact tracing and local surveillance. This early testing strategy helped the State to reduce the total number of infections over time. Other States/UTs such as Maharashtra, Gujarat, Delhi, Tamil Nadu and Madhya Pradesh have meanwhile experienced higher case loads despite increasing testing over time, after having missed the bus early. Only a significant increase in testing and isolation of positive cases will help, short of other possibilities such as increased immunity or the availability of a vaccine. In Kerala's case, a new influx of migrants from other States and countries has made it imperative for the State to also focus on ramped up testing to address the new wave of infections.

*Doubling time - Time taken for cases to double in the last 10 days.

^Stringency index is calculated based on 17 indicators including school closures, restrictions of movement, etc. The index was created by Oxford University

Data sources: Johns Hopkins University, ICMR, India's State health departments

Published - June 01, 2020 04:07 am IST