Covid-19: Why Delhi needs to ramp up testing again

A rising positivity rate typically suggests that a region is testing inadequately. The positivity rate should drop to 5% or below if the testing programme is adequate and is keeping the outbreak in control, according to the World Health Organization.
The average positivity rate over time dropped to as low as 5.3% for the week ending October 8.(Raj K Raj/HT PHOTO)
The average positivity rate over time dropped to as low as 5.3% for the week ending October 8.(Raj K Raj/HT PHOTO)
Updated on Oct 27, 2020 09:02 AM IST
Copy Link
Hindustan Times, New Delhi | By

After appearing to drop for a second time, new infections of the coronavirus disease (Covid-19) in Delhi have started rising again over the past two weeks. This spike in cases has come hand-in-hand with a steady rise in the positivity rate, suggesting that the outbreak may be expanding again.

A rising positivity rate typically suggests that a region is testing inadequately. The positivity rate should drop to 5% or below if the testing programme is adequate and is keeping the outbreak in control, according to the World Health Organization. That is why testing enough, and using the right kind of tests, is the key to Delhi being able to control the outbreak in the next few weeks.

1. A distinct third surge in new infections

The case trajectory in Delhi shows three distinct surges. The first started in mid-June, and peaked when the seven-day average of daily cases, also known as the case trajectory, touched around 3,400 in the last week of June. This dropped to about 1,000 a day by the end of July. It remained in that range for a month, and the second surge started towards the end of August, rising till the middle of September, when average daily cases touched 4,174 – the highest the case trajectory has been so far.

A strong upward trend is now visible for a third time. Average cases have been rising for 13 straight days – from 2,661 on October 12 to 3,663 on Friday. The rising graph of cases in the city – days after it was starting to come under control – has come right at the heels of the festive season, and is being attributed to more people coming out of their homes, poor mask discipline, and lack of adherence to safety protocols due to Covid fatigue.


2. Low testing caused drop between 2nd, 3rd surges

After the first peak ended,and the daily cases went down to 989 (August 5) and positivity rate to 5.8% (August 13), Delhi appeared to make a crucial mistake by easing off on testing, instead of ramping up further to suppress the virus.

This led to a gradual increase in positivity rate over time, and consequently in daily cases, prompting the situation to reach a point on August 26 (1,693 cases, 8.5% positivity rate), when chief minister Arvind Kejriwal held an emergency meeting and decided that the rate of testing would be doubled from 18,000-20,000 daily.

This was a crucial intervention -- on average there were a just little over 20,000 tests being conducted daily at the start of September, and by September 20 this was up to nearly 60,000 tests -- leading to a spike in cases (since more tests were being conducted) but bringing down the positivity rate.

The average positivity rate over time dropped to as low as 5.3% for the week ending October 8.

But after touching its peak, tests started to drop again – for the week ending October 9, daily tests were down to 47,612 from the September 20 high of nearly 59,368. October 9 was also the day when the case trajectory dropped to its lowest – 2,574 new cases a day. When placed alongside each other, it is evident that the dip in average daily testing has heavily influenced the drop in average daily infections being reported.


3. Low RT-PCRs led to numbers being suppressed

A key concern even as the Delhi government increased its testing at the start of September was that much of it was through rapid antigen tests, which are cheap, easy to deploy, and give results within 15 minutes. Due to this, the proportion of reverse transcription-polymerase chain reaction (RT-PCR) tests, considered by experts as the “gold-standard”, dropped significantly in the overall test numbers.

In the first 15 days of September, while overall testing rose, the share of RT-PCR tests nearly halved – from 32.3% for the week ending September 1 to 17% for week ending September 16. This may have suppressed the real positivity rate because rapid tests gives high “false negatives” (labelling infected people as uninfected). .

The share of RT-PCR tests, however, has started rising again. In the past week, 28.2% of all tests have been RT-PCR. And this rise has overlapped with the rise in daily cases in the city since fewer positives are being missed. According to the Harvard Medical School, the reported rate of false negatives in antigen tests could be as high as 50%.


4. Rising positivity rate points to a big problem

The positivity rate for Covid-19 has started rising again, with 6.8% samples tested in the past week coming back positive (this is the highest in nearly a month, since 6.95% on September 27). The number was 5.88% the week before, and 5.49% the week before that.

On Sunday and Monday, it went as high as 8.17% and 8.23%.

Positivity rate is a crucial metric as experts say it shows how widespread the virus is in the community, and when coupled with an increase new cases, indicates that the virus is spreading fast.


Testing needs to be increased again to flatten the curve

Delhi’s rising case rate has come right at the start of the festive season. The fact that it is coupled with the positivity rate increasing is further indication that cases may continue to rise.

The silver lining is that testing is moving in the right direction. Both total tests and RT-PCR tests have increased – in fact the city has set new records for RT-PCR tests three out of the last five days.

But if the objective is to bring the overall positivity rate below 5%, and keep it there for at least two weeks to suppress the virus, the time to increase tests in now. Any figure above 7% means that,even if tests may be up, Delhi is again not testing enough. Unless the number of tests is scaled up, with the share of RT-PCR tests staying high, matters could get out of hand again for the first hot spot in India that almost managed to contain its outbreak.


    Jamie Mullick works as a chief content producer at Hindustan Times. He uses data and graphics to tell his stories.

Close Story

Less time to read?

Try Quickreads

  • Maharashtra chief minister Uddhav Thackeray ANI File Photo

    In second half of tenure, MVA govt has its work cut out

    Now with the MVA entering into the second half of its tenure, the immediate task would be to win the local body elections due in a few months. Besides, it needs to speed up the execution of ongoing infrastructure projects, plan new ones, and most importantly, resolve the quota issues for the Other Backward Classes (OBCs) and the Maratha community. Even before the pandemic broke out, the state's financial condition was in bad shape.

  • Besides two pistols, various instruments, including sensor kit, magnet, LNT keys and eight remote car keys were recovered from them. (Representational image/Stock photo)

    ‘Fast & Furious’-inspired heist in Delhi, 3 held for stealing 40 luxury cars

    Three men, inspired by the Hollywood series 'Fast & Furious', stole 40 luxury cars from across Delhi-NCR over the past one month using several high-tech gadgets, including GPS jammers, scanners and remote-control cars and sold them off in expensive deals. The trio were arrested earlier in the day. Police said the men, one of them from Meerut in Uttar Pradesh, are members of the 'Ravi Uttam Nagar gang'.

  • Uttarakhand chief minister Pushkar Singh Dhami said Uniform Civil Code will provide uniformity (in law) to all religious communities. (File Photo)

    Uttarakhand forms panel led by retd SC judge on Uniform Civil Code

    The Uttarakhand government on Friday formed a five-member committee headed by a retired Supreme Court judge to prepare a draft on implementation of Uniform Civil Code in the state. The committee, led by retired Supreme Court judge Ranjana Desai, will comprise social activist Manu Gaur (retd judge), Pramod Kohli, retired IAS Shatrughan Singh and Doon University vice-chancellor Surekha Dangwal, according to an order issued by the home department.

  • Minister of state Rajni Tiwari was the chief guest of the inaugural session of the conference. (Sourced)

    EFL univ, Vidya Bharati hold int’l conference on NEP 2020 in Lucknow

    A two-day international conference on “fulfilling the vision of National Education Policy-2020” got under way here on Friday. English and Foreign Languages University, in collaboration with Vidya Bharati Uchcha Shiksha Sansthan and Samvit Research Foundation, has organised the event. In Prof Kapoor's keynote address, former pro-vice-chancellor, Jawaharlal Nehru University, Prof Kapil Kapoor said the Indian value system lays more emphasis on duties than rights. The Indian civilization, according to him, is knowledge centric.

  • Allahabad University campus. (HT file)

    Allahabad University, colleges to get back to five-days-a-week working from July 7

    Allahabad University and all its constituent colleges will revert to their five-days-a-week working from the new session that will start from July 7. Registrar of the central university Prof NK Shukla has issued a notification in this regard to bring an end to the system of six-days-a-week working introduced to make up for the lost time in academics and research owing to pandemic when the university and its colleges reopened after lockdowns on February 10 earlier this year. “Following the decision to resume five-days-a-week working, now the varsity and colleges would remain closed on Saturdays also,” said public relations officer, AU, Prof Jaya Kapoor confirming the decision of the university administration. However, various departments, centres and laboratories of universities and colleges will remain open for research works, she added.

Story Saved
Saved Articles
My Reads
Sign out
New Delhi 0C
Friday, May 27, 2022