Covid-19: Delhi’s positivity rate below 5% for third day on the trot

With over 81,000 samples tested, Delhi reported 3,419 new cases of coronavirus disease (Covid-19) on Friday, leading to a daily positivity rate of 4.2% – the lowest in 209 days, or since May 10.

The number of RT-PCR tests, considered by experts to be the gold standard of Covid-19 testing, however, dropped from 40,191 on Friday to 35,352 on Saturday – a reduction of 12%. Overall samples tested also dropped from Friday’s 85,003 to 81,473 on Saturday. Friday’s test count was the highest daily testing figure recorded in Delhi till date.

Reverse transcription-polymerase chain reaction, or RT-PCR, tests are significantly better than rapid antigen tests at detecting positive cases – the latter has a higher tendency to give false negative. As a result, the higher the share of RT-PCR tests in overall testing, the more accurate the positivity rate is.

The positivity rate – proportion of samples that return positive among total samples tested – has now remained below 5% for the third consecutive day. On Friday, with 4,067 new cases, the positivity rate was 4.78%, while on Thursday, it was 4.96%.

According to World Health Organization (WHO) guidelines, the spread of the infection in a region that is testing “adequately” is considered to be under control if the positivity rate holds steady at 5% or below for two weeks.

This is the first time since the Delhi government started releasing testing data in March that the positivity rate has remained below 5% for three consecutive days.

“Let us see for how long the rate stays below 5%; if it holds for at least a week, then the situation would be comfortable. Delhi has been carrying out aggressive testing and contact tracing because of which the positivity rate has reduced from over 15% (it was 15.26% on November 7),” Delhi health minister Satyendar Jain said on Friday.

The positivity rate has been seeing a near steady decline from the last week of November, as per the daily health bulletin released the Delhi government.

“The decreasing number of cases and positivity rate is a good sign – they show that we have scaled down from the peak after the festive season. We have to wait to see what the next sero-survey report says, but I think at least 40% to 50% of Delhi residents must have been exposed to the infection after the November peak. With so many already exposed, Delhi should not see such a high peak again,” said Dr Shobha Broor, former head of the department of microbiology, All India Institute of Medical Sciences.

On Saturday, Delhi added 77 more deaths due to the infection, tipping the city’s total toll beyond 9,500. So far, 9,574 people have died of the infection since the first case was reported on March 2.

The number of deaths being reported daily has dropped to an average of 82 per day over the last seven days as compared to an average of 104 the week before and 107 the week before that. However, with fewer cases being reported, the seven-day average case fatality ratio (CFR) – proportion of deaths among those who test positive – has crossed 2% for the first time since August beginning.