The state of rapid antigen tests: Positivity rate stands at 12.28%
FROM JULY 3 Mumbai’s positivity rate is 6%, compared to 13% in suburbs; state says no. will dip; experts warn against overuse
MUMBAI: More than a month after the introduction of rapid antigen tests to boost testing in Maharashtra, the state’s positivity rate, which indicates the prevalence of Covid-19 infection, using the kits stands at 12.28%, according to the data from the state health department.
Rapid antigen tests involve checking nasal swab samples for antigens (foreign substances that induce an immune response in the body) that are found on or within the virus Sars-cov-2 that causes Covid-19 virus. It is performed outside the conventional laboratory setting, and gives results within 30 minutes. RT-PCR, the gold standard for Covid testing, takes over eight hours. According to protocol, every positive report from the rapid antigen testing is be treated as ‘true positive’, while negative samples of symptomatic people will have to be mandatorily re-tested by RT-PCR process. Positivity rate is the percentage of people testing positive compared to the total tests.
Of the 675,035 individuals tested across 36 districts in the state till August 13, 82,868 have tested positive for the presence of novel coronavirus. A total of 56,852 individuals have been tested with antigen kits in Mumbai city and suburbs, of which 3,350 have tested positive – a positivity rate of 6%. In the rest of the state, high positivity rates were recorded in Ratnagiri (37.20%) and Parbhani (32.47%), despite fewer cases compared to other parts of the state, a cause for concern for government officials.
Mumbai city, once the epicentre of the Sars-cov-2 virus outbreak, has recorded a positivity rate of 6% which is among the lowest in the state, while it is almost 13% in Mumbai suburbs. Health experts said the difference in positivity rate in the city and suburbs is because the pandemic curve has shifted to the outer boundaries of the main city. “A positivity rate of 12% in the state is on the higher side because Delhi has around 7% positivity rate using rapid antigen tests. As many districts like Pune and Thane are at the peak of the pandemic curve, it is expected to have a higher positivity rate. It will come down gradually, just like Mumbai,” said a senior officer from the health department.
The city comprises areas from Churchgate to Bandra on the western railway line, CST to Sion on the central line and CST to Chunabhatti on the Harbour line. Mumbai suburbs extend between Khar and Dahisar on the western line, Kurla to Mulund on the central line and Kurla to Mankhurd on the harbour line.
The Brihanmumbai Municipal Corporation (BMC) with the intention of testing aggressively to identify people with Covid-19 started the antigen tests from July 3. Till August 13, 50,462 people underwent the test in Mumbai city, of which 2,531 tested positive. During the same period, in Mumbai suburbs, 6,390 took the test, and 819 came positive. “When the pandemic started, it was mainly limited to south Mumbai with international travellers, but gradually started to spread. Now, the suburbs have more active cases than town, which explains the high positivity rate. With the gradual unlocking of the lockdown, the movement of people has increased. Thus, the virus which was limited till south and central Mumbai has shifted to the northern side,” said Dr Shashank Joshi, part of the state’s Covid-19 task force. “The test has helped us increase daily testing to more than 10,000 samples. Earlier, we started it in the northern wards of Mumbai and a few Covid-19 specific hospitals, but now, it is being conducted in all wards. Unlike RT-PCR, it is easier to use and we have plans to procure more kits,” said Suresh Kakani, additional commissioner, BMC.
Dr K Srinath Reddy, president, Public Health Foundation of India, warned against overuse of the kits. “As per ICMR (Indian Council of Medical Research), antigen tests have a moderate sensitivity of around 50%. So, if we start using it more than RT-PCR, we might lose many infected patients” he said.
Ratnagiri, a port town which is around 350km away from Mumbai, has recorded 2,449 Covid-19 cases since March, far lower than Mumbai, but it the highest positivity rate in the state. Till August 13, 414 people were tested using the kits, of which 154 (37.20%) were positive. Health officers attributed the high positivity rate to the presence of more number of asymptomatic patients.
Dr Kamalpurkar, district health officer (DHO), said, “We are getting maximum number of positive cases from containment zones and hospitals. Despite having lower number of Covid-19 cases, we are trying to expand our daily testing of antigen kits for faster diagnosis.” It is followed by Parbhani with 32.47% positivity rate (661 of 2,036 tested positive). It is followed by Pune. Of the 124,533 tests, the highest in the state, 28,447 (22.84%) came positive. Kolhapur stands fourth with 21.81% positivity (1,116 of 5,117 positive). Jalgaon recorded 20.29% positivity rate, with 3,729 of 18,382 coming positive.