Mumbai civic corporation says daily Covid-19 tests surged to 15,000 from 10K in last week of AugustUpdated: Sep 16, 2020 00:43 IST
The Brihanmumbai Municipal Corporation (BMC) has steadily increased the number of tests conducted for Covid-19 this month. In the second week of September, Mumbai conducted up to 15,000 tests per day, of which up to 40% were rapid antigen tests and the remaining were reverse transcription polymerase chain reaction (RT-PCR) tests. This is a sharp increase from the last week of August, when 7000 to 10,000 tests were conducted per day, of which up to 28% were rapid antigen tests. So far, Mumbai has conducted 9,25,148 tests and its positivity rate is 18.34% at present.
BMC’s data shows that compared to the first week of September, when approximately 67,500 tests were conducted, there was a jump of approximately 20% in the second week of September, when approximately 81,500 tests were carried out. In the last week of August, BMC conducted approximately 60,100 tests, which was 45% more than the number of tests carried out in the first week of August (approximately 26,800). Along with the number of tests, the percentage of rapid antigen tests has also risen. In July, when the city saw 5,000 to 7,000 Covid-19 tests daily, rapid antigen tests were 10% of the total.
Dr Shashank Joshi, a member of Maharashtra’s Covid-19 taskforce, said, “We still need to do more tests to control the spread of the virus. Also, we need both methods – rapid antigen kits and RT-PCR – considering rapid antigen is required for its fastness. We can always go for the RT-PCR method if those suspected test negative in rapid antigen tests.”
While RT-PCR tests are considered the gold standard for Covid diagnosis, it takes several hours to arrive at results. In contrast, results of rapid antigen tests can be delivered in approximately 30 minutes. However, rapid antigen tests continue to have a low positivity rate (between 5% and 10%, with a few exceptions) while RT-PCR has a high positivity rate of between 20% and 30%. Positivity rate is the percentage of people correctly diagnosed as Covid-positive from the total tests conducted.
The low positivity rate for antigen tests means that on when Mumbai saw more of these tests being conducted, the positivity rate for the day also dropped. For example, on September 9, Mumbai conducted 15,700 tests of which 7,300 were rapid antigen tests. The city’s positivity rate for the day was approximately 16%. Similarly, on September 19, Mumbai conducted 15,100 tests of which 6,700 were rapid antigen tests, and the city’s positivity rate was 17%. In contrast, on September 13, Mumbai conducted 9,400 tests of which 1,900 were rapid antigen tests, and the recorded positivity rate was 24%.
Since antigen tests deliver quick results, they are preferred in cases where a suspected Covid-19 patient may have a high number of risk contacts. Last week, BMC commissioner Iqbal Singh Chahal had told HT, “Rapid antigen kits have to be used for suspicious patients who have heavy symptoms. We cannot use the kits randomly on say citizens or frontline workers. The positivity rate for RT-PCR is much more but this doesn’t mean we will not use rapid antigen kits.”
BMC has already used more than 1 lakh rapid antigen kits till now, and has ordered more rapid antigen kits.
A senior officer from BMC said, “BMC started out using rapid antigen kits for shopkeepers, frontline workers, in slums, and high risk contacts of Covid-19 patients. Because we get immediate results, it helps to quarantine suspected patients immediately and break their contact with the community. We will use rapid antigen kits for repeated testing of frontline workers with greater interaction with the community.”