31% of Maharashtra’s total Covid-19 tests done using antigen kits

Account for more than 60% of daily tests in Maharashtra; experts warn against over dependence

Although the use of rapid antigen tests in Maharashtra began in July, the diagnostic tool already accounts for 31% of the total Covid-19 tests, with more than 60% of the daily tests in Maharashtra being carried out using the kits, according to the state health department data.

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The rigorous reverse transcription polymerase chain reaction (RT-PCR) test is considered the gold standard for Covid testing. RT-PCR test results come in eight hours, while antigen tests give results in 30 minutes and are considered less reliable in comparison. RT-PCR test is carried out on symptomatic patients and those who come negative in the antigen test. Medical experts advise against over dependence on antigen tests due to its high false negative rate.

Since the Covid-19 outbreak in March till September 7, Maharashtra has conducted 4,705,932 tests, of which 1,458,827 were antigen tests. The data, accessed by HT, shows that every day, 45,000-50,000 rapid antigen tests are conducted in Maharashtra, while around 25,000-odd tests are through RT-PCR. For instance, 46,961 of the total 72,248 tests conducted on September 2 were through rapid antigen-based kits. While less than 5% were TrueNat tests (originally designed to test tuberculosis), the remaining tests were via RT-PCR.

Maharashtra, which is one of the worst-affected states, has one-fourth of India’s active cases. To boost testing, public health officials have asked all hospitals to use antigen tests as a primary testing tool to detect Covid-19 patients with severe acute respiratory infection or influenza-like illnesses. They have also recommended the use of antigen tests for high-risk contacts of patients and symptomatic healthcare workers.

In a rapid antigen test, oral or nasal swab samples are taken to detect the presence of antigens (foreign substances that trigger antibodies inducing an immune response in the body) that are found on or within the Sars-CoV-2 virus that causes Covid-19. Unlike RT-PCR, the biggest advantage of this rapid point-of-care testing method is that it can be performed on the spot and outside a conventional laboratory setting, as it doesn’t deal with a live virus, and gives results within 30 minutes. RT-PCR tests for genetic material of the Sars-CoV-2 virus and therefore needs a biosafety level 2 laboratory for analysis, and provides results in five to eight hours.

The data shows that on August 2, 50,421 of the 78,711 tests were antigen tests. Again, 40,905 of the 68,175 tests conducted on August 28 were through antigen kits.

Districts like Mumbai, Pune, Thane, Aurangabad, Nashik, Nagpur and Solapur are conducting maximum number of rapid antigen tests in the state, which is spending around ₹1 crore every day.

“We are not overdoing rapid antigen tests in the state. We are focussing on 50:50 ratio for antigen tests and RT-PCR. In fact, if any person with symptoms tests negative in the state, we run a second confirmatory test under RT-PCR. The false negative reports are not even 1%,” said Dr Pradeep Awate, state surveillance officer.

According to the Indian Council of Medical Research’s (ICMR) June 14 ‘Advisory on Use of Rapid Antigen Detection Test for Covid-19’, sensitivity (or the ability to detect true positives) of antigen tests ranged from 50.6% to 84%. “This implies that half of the negative reports given by rapid antigen tests may be incorrect. Also, considering 80% of people in India are asymptomatic, we will miss out on a large number of silent carriers due to ICMR rule [of RT-PCR tests for symptomatic people who test negative],” said Dr K Srinath Reddy, president, Public Health Foundation of India.

Recently, after veteran actor Amitabh Bachchan and his son Abhishek tested positive for Covid-19 following the onset of mild symptoms, other family members — actor Aishwarya Rai Bachchan and daughter Aaradhya — who did not display symptoms tested negative through antigen tests, the first line of testing. Later, in RT-PCR, the duo, who continued to be asymptomatic, tested positive for Covid-19.

“This is why antigen tests are more likely to miss an active coronavirus infection,” said Dr Avinash Bhondwe, president of Indian Medical Association (IMA), Maharashtra.

Healthcare experts said that while a testing strategy combining RT-PCR and antigen tests is a good decision, they warn that antigen tests should be restricted to containment zones and specific cases.

“Antigen kits can prove effective in containment zones and faster diagnosis of suspected patients with SARI (severe acute respiratory illness) and ILI (influenza-like illness). But deployment of antigen tests for mass-based diagnosis is debatable. The more we increase the testing, the chances of kits throwing up negative results in asymptomatic patients gets higher,” said Anant Bhan, public health expert.

As HT reported on August 15, amid scepticism over high false negatives in the rapid antigen test, state government data showed that a mere 0.17% of the samples tested in Maharashtra failed to identify the presence of the Sars-Cov-2 virus.

At present, the state has 156 Covid-19 government accredited testing laboratories. But medical experts from the state’s Covid-19 task force said despite increasing testing capacity, it was only through antigen testing that they could bring testing facilities closest to the public as it doesn’t need laboratory set-ups. “In the early stage of the pandemic, when we relied only on RT-PCR, laboratories were getting overwhelmed with samples. Some laboratories even took two-three days to provide the reports which delayed treatment. At least, with antigen tests, people are getting reports on time,” said a senior health officer who requested anonymity as he is not authorised to speak to media. “Our focus is to identify super spreaders.”

In Mumbai, 95,342 antigen tests were conducted till September 8. The Brihanmumbai Municipal Corporation (BMC) has ordered another one lakh testing kits. “So far, we have concentrated only on running antigen tests in Covid Care Centres (CCC) and hospitals along with containment zones. But now, we will extend the testing to civic-run peripheral units and dispensaries,” said Suresh Kakani, additional commissioner, BMC.

Considering the growing demand, ICMR has evaluated 23 brands of antigen test kits. Three of them have been approved— SD Biosensor, LabCare Diagnostics and Coris Bioconcept. The health department can procure any of the three approved kits through the Union health department, while private hospitals can buy it from approved vendors.