Anonna Dutt



Delhi’s positivity rate—the proportion of samples that test positive—has remained at 5% or less for six days in a row, with the city testing over 74,000 samples for coronavirus disease (Covid-19) on average every day.

The positivity rate dropped to 3.10% on Monday as per the health bulletin released by the government. The city reported 1,647 new cases of Covid-19 on Sunday when a lower than average 53,207 samples were tested.

There were 63 deaths due to the viral infection, taking the total toll of the city so far to 9,706. The number of deaths has remained below 100 a day for seven days now, yet the seven-day average case fatality ratio (CFR)—the proportion of deaths among those who test positive—continues to climb as fewer cases are reported.

The seven-day average CFR in Delhi was 2.35% on Monday as compared to 1.93% a week ago, when 108 deaths and 3,726 cases were reported in a day.

“In a month positivity declined to 3.15% today from 15.26% on 7th Nov. During the same period RTPCR positivity reduced to 6.68% from 30.20%. Lowest positivity in last 6 months. Steadily corona cases and positivity coming down. Hope this will continue. Please observe all precautions,” Delhi health minister Satyendar Jain tweeted.

Experts believe that the spread of the infection is under control when the positivity rate is 5% or less for two weeks.

The data breakup of RT-PCR and rapid antigen tests shared by the minister on Twitter showed that on average, from November to December 6, RT-PCR tests detected 2.5 times the number of cases that rapid antigen tests detected, even though RT-PCR tests accounted for less than 40% of the total administered.

“It is very encouraging to see that the positivity rate in Delhi has remained below 5% for almost a week, especially since the government has increased the number of the more accurate RT-PCR tests. However, this does not mean that the government can scale down the number of tests. If the current number of tests is maintained and the positivity rate continues to remain low, it will instil confidence in people that the number of infections has gone down,” said Dr Lalit Kant, former head of the department of epidemiology and infectious diseases at the Indian Council of Medical Research.

The RT-PCR tests constituted over 45% of the tests administered over the last fortnight as compared to around 37% the fortnight before.

Molecular tests such as RT-PCR amplify the genetic material of the virus to detect its presence in a patient sample, making them more accurate than rapid antigen tests. Rapid antigen tests are cheaper, easy to deploy outside of labs and take only 15 minutes to give results, but they are known to throw up false negatives for nearly half the patients who might have the infection.