Delhi sees 3,579 new Covid cases, highest in 25 days

So far, the infection has affected over 336,000 people in the city and killed 6,081. The city on Tuesday had 23,922 active virus cases.

Delhi reported 3,579 new cases of coronavirus disease (Covid-19) on Tuesday, the highest in 25 days. The number of cases of the infection has been on the rise again in the city, with over 3,000 cases being reported each day in the last week, barring Sunday, when comparatively lesser number of tests were conducted .

A woman reacts as a healthcare worker collects a swab sample amidst the spread of the coronavirus disease (Covid-19), at a testing centre, in New Delhi. (Reuters)

So far, the infection has affected over 336,000 people in the city and killed 6,081. The city on Tuesday had 23,922 active virus cases.

Not only the absolute number of cases, the positivity rate – proportion of samples that return positive among total tested – has also been on the rise. Delhi‘s has notched an average positivity rate of 6.1% over the last seven days, as compared to 5.5% the week before and 5.4% the week before that..

The number reflects ongoing transmission of the infection, with a positivity rate of less than 5% maintained over two weeks, an indication of control of the spread.

On an average, 13,900 RT PCR tests were done each day during the last seven days, as compared to 10,471 the week before, and 9,536 the week before that. At its highest – October 16 – the city conducted 15,660 RT-PCR tests.

The RT-PCR tests accounted for about 26.5% of the total tests that were done during the last seven days. This is higher than the 21.7% of the total tests it accounted for the week before and 19.2% the week before that.

The alternate for the government is using rapid antigen test — which is cheap, easy to deploy in clinics and dispensaries, and gives results within 15 minutes. However, the rapid antigen tests are much more likely to throw up false negative reports for people who might actually have the infection.

“The sensitivity – or the ability of a test to detect true positive cases – is as low as 50% in rapid antigen tests depending on how samples are collected. This is much higher for an RT-PCR test at about 80 to 85%. It could be lower – on average 70% -- depending on how the sample was collected, how it was transported, and how many probes were used in the test. But it will pick up more cases than the rapid antigen test. So, if you increase the number of RT-PCR tests, the number of cases and positivity rate is likely to go up,” said Dr GC Khilnani, former head of the department of pulmonology at the All India Institute of Medical Sciences (AIIMS).