Covid-19 in Mumbai: BMC relies more on antigen tests since September

Civic body says ratio changed, but no. of RT-PCR tests has not dropped drastically; experts say not ideal

Amid the fear of a second Covid-19 wave, the city’s civic authorities are relying more on the less-dependable, but quick-result Rapid Antigen Tests (RATs) than the Reverse Transcription-Polymerase Chain Reaction (RT-PCR) tests, considered the gold standard in detecting the presence of the novel coronavirus, the pathogen responsible for Covid-19.

Rapid antigen tests being conducted at Dadar.(Anshuman Poyrekar/HT Photo)

According to the Brihanmumbai Municipal Corporation (BMC) dashboard, of the 3.52 lakh tests conducted in September in Mumbai, 69% were RT-PCR while the remaining were done using RAT kits. In October, of the 4.07 lakh tests, 60% were RT-PCR and 40% RATs. In November, the usage of RT-PCR kits was at its lowest in three months. Of the 3.59 lakh tests in November (up to November 29), 54% were through the RT-PCR method and 46% via rapid antigen kits. While the positivity rate (the number of people that test positive out of every 100 tested) of RT-PCR tests is between 10% and 12%, the positivity rate of antigen tests is only 3% or 4%.

Mumbai is testing anywhere between 12,000 to 19,000 samples every day. BMC, however, maintains its RT-PCR testing capacity is around 15,000 samples a day.

Civic officials also claim that the actual number of RT-PCR tests has not dropped drastically, although the ratio may have changed, and that every symptomatic citizen testing negative via rapid antigen kits was made to undergo RT-PCR test. Its data substantiates the claim.

In 30 days of September, 2.42 lakh tests were performed using RT-PCR and 1.09 lakh using rapid antigen kits. In 31 days of October, the number of RT-PCR tests went up to 2.43 lakh, with 1.64 lakh rapid antigen kits. However, in November (up to November 29) the number of RT-PCR went down to 1.97 lakh, compared to 1.62 lakh rapid antigen kits.

Mumbai recorded 58,195 cases and 1,236 deaths in September; 50,006 cases and 1,281 deaths in October, followed by 25,052 cases and 535 deaths in November (up to November 29).

Suresh Kakani, additional municipal commissioner, said, “There is no change in the testing strategy of the BMC. RT-PCR still remains the gold standard, and we are scaling up our capacity of conducting RT-PCR tests. But the overall positivity rate of RT-PCR kits has also gone down to 10-12% now; this was much higher two or three months ago, which helps in reducing the overall positivity rate.”

Kakani added, “The ratio proportion for RT-PCR tests may have gone down, but there is no huge fall. We are constantly increasing testing, if you see the overall data. However, in the past two months, a lot of curbs have been lifted. Due to this, we need instant results and rapid antigen kits are preferred. We have set up free testing centres, and are conducting free testing for hawkers, BEST bus drivers and other citizens that have multiple contacts, including passengers coming from Rajasthan, Gujarat, Delhi and Goa. Even here, symptomatic citizens testing negative in rapid antigen kits are being tested via RT-PCR.”

Overall, since February 3, over 18.96 lakh samples have been tested, of which, according to BMC, 30% are using rapid antigen kits, as of November 29.

The testing figures have drastically increased in the city post July 7, when the BMC liberalised testing.

Due to this, any citizen irrespective of being symptomatic or not can get tested for Covid-19. The one-lakh-test mark was crossed on May 6, four lakh on July 14, five lakh on July 29, eight lakh on September 3, and the 10 lakh on September 22. In the next two weeks, Mumbai is set to cross the 20 lakh mark.

Experts feel the BMC should focus both on increasing Mumbai’s testing and also ensuring a balance between RT-PCR and rapid antigen kits testing in order to handle the positivity rate and fatality rate better.

Dr Rahul Pandit of Fortis Hospital, a member of Covid-19 task force of Maharashtra, said, “As a member of the task force, I strongly feel that maximum testing should be done using the RT-PCR method. Rapid antigen kits should only be used on patients who are in the hospital with symptoms of Covid-19. Rapid antigen kits cannot be used for the general public. However, in Mumbai, the rapid antigen kits ratio at times is around 45-55%, which should not be the case.”

Dr Om Shrivastava, a member of Maharashtra’s Covid-19 task force, said, “I feel we should test 10 to 30 times behind every positive case. For example, if we are saying on Monday, the city had around 600 cases, we should be testing at least 25,000 samples daily.”

Another member of Maharashtra’s Covid-19 task force, Dr Shashank Joshi, said, “The ratio of rapid antigen testing went up because Mumbai’s capacity to test using RT-PCR method saturated. We need to add more RT-PCR testing facilities in Mumbai. That is the reason why the ratio of RT-PCR to rapid antigen appears to have changed over September, October and November.”

“We need to continue testing as we unlock more so that we diagnose and treat faster quicker and reduce our test positivity rate and improve our case fatality rate,” he said.