New Delhi: Since the announcement of the lockdown on March 24, 2020, India has tested over 3.3 million samples for SARS-CoV-2, the virus that causes COVID-19. Its daily testing has increased by a factor of 65, from about 1,800 tests on March 24, 2020, to 119,976 tests on May 28, 2020. During the same period, India’s case count rose from 536 to 158,333, with 6,566 new cases reported on May 28, 2020. Between April 14 and May 27, confirmed cases increased at a 6.4% daily rate, outpacing the 5.9% daily increase in samples tested, despite widespread calls to rapidly expand testing.

Only 36% of these 3 million tests have taken place in the four states where 67% of India’s confirmed cases have been detected--Maharashtra, Tamil Nadu, Gujarat and Delhi. Between April 14 and May 27, 2020, in the most affected states, the number of samples tested increased at an average daily rate of 6.2%, slower than the daily case growth of 7%.

Tamil Nadu, which has conducted the most tests in the country, had tested 443,970 samples and confirmed 18,545 cases by May 27, 2020. Maharashtra, India’s worst-affected state, had tested fewer samples, 403,976, to confirm more than three times as many cases at 56,948, based on figures reported as of May 27, 2020.

Between April 14 and May 27, 2020, the increase in the number of samples tested and cases confirmed has followed a similar trajectory in Maharashtra, Delhi and Gujarat. While the daily rate of increase in cases averaged at 7.1%, the number of samples tested increased by 5.6% every day, on average, in these states during this period. These figures are based on three-day moving averages of testing and case statistics to smooth daily fluctuations.

Increase in testing outpaced case growth in Tamil Nadu during April 2020. Between April 14 and April 30, 2020, confirmed cases increased by 92%, rising from 1,204 to 2,323, while the number of samples tested increased by five times, growing from 19,255 to 119,748 in the same period. Thus while cases grew at a 4% daily rate, on average, the number of samples tested rose by 12.6% every day.

In May 2020, the trend in Tamil Nadu started to resemble that in other states, with samples tested growing at a slower daily rate of 5.2%, on average, compared to a daily increase of 8.4% in confirmed cases.

Total Confirmed Cases Versus Samples Tested, April 14 and May 27

Source: National data from the Indian Council of Medical Research. State data from health departments: Maharashtra, Tamil Nadu, Delhi, and Gujarat.
Note: Delhi state health bulletins for April 30 and May 1 did not include data on testing

Overall, India tests 2.4 samples for every 1,000 people, the lowest rate in worst-affected countries. The number of samples tested per confirmed case fell from 26 on April 14 to 21.4 on May 27, 2020, a reflection of the slower growth of testing versus confirmed cases.

All four states have been testing at a rate higher than the national average. Maharashtra’s testing rate is 2.9 per 1,000 population, Tamil Nadu’s 5.3, Delhi’s 8, and Gujarat’s 2.9. Of these four states, only Tamil Nadu’s positivity rate is lower than the national average. It tests 26.4 samples for each confirmed case. Maharashtra finds a positive result for every 7.7 samples, Delhi 14.2, and Gujarat 20.2.

(Bharadwaj, an undergraduate at Yale University, is an intern with IndiaSpend.)