Highest number of tests, second lowest positivity rate in over 200 days

The Capital conducted a record 85,105 tests for the coronavirus disease (Covid-19) on Tuesday, as authorities continued to ramp up testing, even as the number of

The Capital conducted a record 85,105 tests for the coronavirus disease (Covid-19) on Tuesday, as authorities continued to ramp up testing, even as the number of cases continued to decline and the positivity rate plummetted. Almost half – 42,056 – of all tests on Tuesday were conducted using the more accurate RT-PCR method, also the highest number Delhi has seen so far.

HT Image

Before Tuesday, the most reverse-transcription polymerase chain reaction (RT-PCR) tests conducted in a single day in Delhi were 40,191 on December 4.

Even with the record number of tests, the city saw just 1,617 new cases of Covid-19, bringing down the positivity rate to 1.90% — the second-lowest since the Delhi government started providing testing data consistently. Experts have warned that if the RT-PCR tests slacken, it could catch the Capital off guard if the outbreak begins resurging.

Delhi has now added an average of 1,950 new cases of the infection over the past seven days, down from 3,247 in the week ending December 7.

The positivity rate — the percentage of positive cases out of all tests conducted — is regarded by experts as a crucial metric to assess an outbreak in a community.

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 two weeks before an outbreak is considered under control.

The lowest daily positivity rate so far was recorded 254 days ago on April 6 when 1.16% of the samples were found to be positive.

The average positivity rate over the past seven days has been 2.66%, down sharply from 13.58% in the second week of November when the Capital was in the throes of the third wave of infections, and daily infections consistently crossed the 7,000 mark.

The city recorded 41 deaths due to the viral infection as per the daily health bulletin released by the government. This takes the seven-day average case fatality ratio (CFR) – proportion of deaths among those who test positive – to 2.48%.

“Delhi has the least case fatality ratio at 1.6, comparatively, Ahmedabad is at 4.0, Mumbai at 3.8, Kolkatta at 2 and Chennai at 1.8,” the Delhi health minister Satyendar Jain had tweeted.

“People are still going out, there are weddings, people are not wearing masks or maintaining social distance and yet the numbers and positivity rate have continued to decline. This seems to be an indicator that most of the people in the city have been exposed to the infection. In the absence of behavioural change, that seems to be the most logical reason for why the numbers are going down, especially after a surge like the one in November,” said Dr Shobha Broor, former head of the department of microbiology at the All India Institute of Medical Sciences (AIIMS).

She feels that the number of cases is unlikely to spike again to the levels in November, unless the virus mutates significantly.

With fewer new cases, the number of active cases, or those currently infected, also dropped below 15,000 on Tuesday — the first time since August 31.

The Delhi government has scaled up testing to around 71,800 samples a day on average over the last week. This has increased from an average 52,617 tests conducted a day during the first week of November.

After a meeting with the Union home minister Amit Shah in mid-November, the Delhi government said it planned to scale up testing to between 100,000 and 120,000 a day, at least half of which would be done using RT-PCR tests. The alternate rapid antigen tests are cheaper, easy to deploy outside lab settings, and give results within 15 minutes. However, they are also less accurate and can detect only around half of positive cases correctly.