50% Covid-19 tests in city in December were using rapid antigen kits, says Mumbai civic body
The monthly share of less-dependable, but quick-result rapid antigen tests in the city is on the rise, compared to 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, according to the Brihanmumbai Municipal Corporation’s (BMC) data. The antigen tests give results in 30 minutes, whereas RT-PCR tests take eight hours.
Of the 4.48 lakh tests conducted in Mumbai in December (until December 30), 2.21 lakh (49.37%) were using rapid antigen kits, while 2.27 lakh (50.62%) were RT-PCR tests. In November, 1.68 lakh (45%) of the 3.71 lakh tests were using antigen kits, while in October, of the 4.07 lakh tests, 1.64 lakh (40%) were using antigen kits. The BMC conducted 3.51 lakh tests in September, of which 1.09 lakh (31%) were using antigen kits. Conversely, the ratio of RT-PCR tests dropped from 69% in September to 60% in October and 55% in November.
Experts from the state-appointed Covid-19 task force say the scenario is not ideal and the government should rely more on RT-PCR tests to control the pandemic. Civic officials, however, say that every symptomatic citizen testing negative via rapid antigen kits is made to undergo RT-PCR test for confirmation of the infection.
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. The BMC, however, maintains its RT-PCR testing capacity is around 15,000 samples a day.
The BMC has maintained that the usage of rapid antigen kits has not affected the positivity rate. In December, the city reported only 9,245 cases and 223 deaths, compared to 25,062 cases and 566 deaths in November, and 50,006 cases and 1,281 deaths in October.
Dr Shashank Joshi, member of Maharashtra’s Covid-19 task force, said, “We can’t conclude that the positivity rate is going down due to increased use of rapid antigen kits, however, RT-PCR test remains the gold standard. We are very near 50:50, and this is not ideal. I would say the ratio of RT-PCR to rapid antigen tests should be 80:20.”
Dr Joshi added, “Use of rapid antigen kits has also increased because of more unlocking, as we need quick results. But this can also be done by using advanced technology to get results of RT-PCR tests. Rapid kits are a good screening tool, but RT-PCR is better for diagnosis.”
Dr Rahul Pandit of Fortis Hospital, another member of the task force, said, “Ideally, 70% tests should be conducted using the RT-PCR method, while 30% using the rapid antigen kits. The current ratio of 50:50 is not ideal…We can confirm that use of rapid antigen kits is increasing due to unlock only when we have segregated data of how many times the rapid antigen kits were used for screening and how many times for diagnosis. If not, we should not simply assume unlocking to be the reason.”
Dr Mangala Gomare, chief of BMC’s public health department, said, “I can’t comment without going through the data. However, we are conducting sufficient RT-PCR and rapid antigen tests.”