Does lower testing in Delhi point towards a lowering of guard?
Delhi conducted 21,660 daily tests at an average for the week ending July 9, what has been the city’s highest recorded rate of testing till date.Updated: Aug 15, 2020 06:28 IST
Testing for the coronavirus disease (Covid-19) in Delhi appears to have dropped from its peak levels, raising questions about whether the Capital is lowering its guard too soon in its efforts to contain the pandemic, after becoming the first major hot spot in the country to successfully rein in the outbreak last month.
Delhi conducted 21,660 daily tests at an average for the week ending July 9, what has been the city’s highest recorded rate of testing till date. Since then, this number has dropped to 18,491 in the past week — down by around 15%. In the same period, the national average of daily tests has increased from 246,677 a day on July to 700,860 — up by around 184%.
The government attributes this dip to factors such as inclement weather and public holidays.
“The number of tests done on some days is lower. This is mainly because people do not come to the dispensaries or hospitals. For example, yesterday it was raining for most of the day and people did not come. Or, there were holidays like Rakshabandhan or Eid during which people do not want to step out. We are prepared, no one is refused a test if they need it,” said Delhi health minister Satyendar Jain.
Indeed, Delhi’s deputy chief minister Manish Sisodia, in an interview to HT on July 1, said the city was heading to 40,000 tests a day. “This is the benefit of rapid testing — you can do it at a large scale. You cannot scale up RT-PCR to that level. We are moving towards 40,000 tests a day. And, the day we do that, it is possible that 4,000 people will test positive, I am prepared for that,” he said. Delhi had started scaling up the tests mid-June. In the first week of June, Delhi was testing 5,500 samples a day.
Instead of scaling up, however, the data suggests that Delhi’s testing number is dipping.
Daily testing in the rest of the country has touched at an all-time high, particularly since Indian Council of Medical Research (ICMR)’s decision to set a target of testing a million samples a day. HT reported on Friday that the national scale-up of testing appears set to meet the target in 12 days.
To be sure, Delhi has consistently had one of the highest testing rates in the country. The city has conducted over 63,000 tests per million residents against the national average of 20,778.
The Capital was the first major hot spot in the country to have successfully reined in the outbreak last month. At the end of June, the city was reporting over 3,400 cases every day at an average, which has since dropped to 1,100 as of last week.
“Scaling down testing is not an option for Delhi as the cases remain high. For testing to be scaled down, you should have a positivity rate of 5% or below for a prolonged period of time,” says Dr Lalit Kant, former head, epidemiology and communicable diseases, ICMR.
Experts also questioned the city’s increasing share of antigen, or rapid tests, which are not as reliable as the gold-standard RT-PCR tests, in the city’s total testing numbers. And they believe that the city should use its spare RT-PCR testing capacity instead of over-relying on antigen tests.
“Yes, we have a capacity to do more tests, but it is like saying I have a capacity to treat 14,000 people. If there are no cases in Delhi, who should admit on these beds? Similarly, the positivity rate of the infection has gone down from 30% to 6%, so we don’t need as many RT-PCR tests,” said Jain.
A senior district official said that RT-PCR tests are largely being used for confirmation only. The first test to be done is a rapid antigen, the official said on condition of anonymity. “This is part of a planned strategy agreed upon by a joint committee on Covid-19 management. Those who are symptomatic and test negative on rapid antigen test are tested using RT PCR,” said a senior official from the health department.
“The tests in Delhi are being conducted strictly as per ICMR guidelines. RT-PCR tests are readily available at all flu clinics, laboratories and hospitals. Anyone who has Covid-like symptoms can visit any of these centres and easily get an RT-PCR test. No problems have been reported where a person who wants to get an RT-PCR test done has been unable to do so,” a Delhi government spokesperson said. “Earlier, when the cases were high more people were visiting these centers to get themselves tested. Now since the number of cases has dipped, the number of RT-PCR tests has also fallen down accordingly.”
The recent stagnation in Delhi’s daily tests is also reflected in a plateau the weekly average positivity rate — the fraction of tests that come back positive — in the Capital. The number, which had dropped from a peak of 31.4% in mid-June to 5.7% at the end of July, has not gone down further. Around 6.2% of tests have come out positive in the Capital for the week ending August 13. Overall, 11.8% of all tests in Delhi have come back positive (the national average is 8.9%).
According to recommendations by the World Health Organization (WHO), the positivity rate from a region that has a comprehensive testing programme should be at or below 5% for at least 14 days before it can be considered that the outbreak is under control in the region. In case the positivity rate rises, WHO recommends increasing testing numbers for prolonged periods of time till the number drops below 5%.
Antigen tests generally provide results within hours and are relatively cheap, but they are not as reliable as the gold-standard RT-PCR tests. The latter is the most definitive test currently available for Covid-19 and experts say should be used to the extent possible, especially if authorities have the capacity to do so.
In Delhi, over 72% of all tests in the past week have been antigen. This is a higher share of antigen tests than what is done elsewhere in the country. Three other states release daily breakup of testing data other than Delhi — Andhra Pradesh, Karnataka and West Bengal. Antigen tests have been roughly half the tests in Andhra Pradesh and Karnataka in the last week, while in West Bengal a third of all tests were antigen. On August 5, senior ICMR officials had said during a media briefing that antigen tests constituted between 25-30% tests of the total tests done in the country till then.
In absolute numbers RT-PCR tests have dropped much below the peak capacity exhibited by city authorities towards the end of June. On June 29, 9,619 RT-PCR tests were conducted in Delhi, the highest single day RT-PCR test count recorded. On August 13, the number of RT-PCR tests was 5,721.
“What is the problem with using antigen testing? No other state is testing as many samples, we are doing well. So people want to find loopholes. What is the problem with antigen testing? Some people say rapid antigen tests are not as sensitive and miss out some positive cases, so does RT-PCR. My first test was negative. In the case of rapid test too, if someone is symptomatic, then an RT PCR test is done for confirmation,” said Jain. “It is so easy to get a test done in Delhi that people from other states are also coming here and getting tested.”
Experts say RT-PCR remains the gold standard as it gives fewer false negatives, but that authorities end up picking test type based on whether they want accuracy or speed.
“RT-PCR is the gold standard of testing because it has higher sensitivity, which means false negatives are less. In containment zones, RT-PCR should be ideally done, and rapid antigen is better suited for cold zones where you don’t expect too many cases. Having said that, rapid antigen testing is more useful for faster results, so there’s no hard and fast rule in this accuracy-verses-speed challenge,” says Dr Kant.
To be sure, the Delhi government has warned against complacency right through, and cautioned residents not to stop using measures such as wearing marks and practising social distancing even though the cases have fallen off their peak.