TB testing machines record 20% Covid-19 positivity rate in Maharashtra

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Published on Aug 31, 2020 12:49 AM IST
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By Rupsa Chakraborty, Mumbai

TrueNat, a portable medical device that was originally designed to detect tuberculosis (TB), was recently used to test 26,000 people across Maharashtra for Covid-19. Of this number, almost 20% tested positive for the novel coronavirus.

This has prompted the state health department to run TrueNat tests for Covid-19 on individuals in need of emergency surgeries since it gives results within 20 minutes.

TrueNat is a chip-based real-time polymerase chain reaction (RT-PCR) test kit that was used as a screening mechanism for potential TB patients. As per Indian Council of Medical Research (ICMR), the diagnostic tool involves two steps — E gene screening assay for suspected Covid-19 samples, and a follow-up confirmatory assay of RNA-dependent RNA polymerase (RdRp) enzyme found in the virus’ RNA (ribonucleic acid). RNA is essential in various biological roles in coding, decoding, regulation and expression of genes.

Since May, 26,215 people in the state have undergone TrueNat tests, of which lab technicians found 7,693 samples had the presence of the E gene. This accounts for 29% positivity rate in the first stage of TrueNat tests. Though actual data is not shared, as per an official from the state health department, more than 90% of samples were found Covid-19 positive in TrueNat RDPR. After completing both steps, the cumulative positivity rate of TrueNat in identifying the Sars-CoV-2 virus, which causes Covid-19, stands at 20%.

“As per ICMR guidelines released in May, if the E-gene screening is negative, the sample will be considered a true negative. But if the sample is positive, the RdRp assay will be done as a confirmatory test. If the sample tests positive, it will be considered a true positive, and no further test will be required,” said Dr Pradeep Awate, state surveillance officer. “So far, we are conducting a limited number of TrueNat tests in comparison to RT-PCR and antigen tests. But we have plans to extend the TrueNat tests,” he said.

TrueNat is an indigenously developed, portable version of cartridge-based nucleic acid amplification test (CB-NAAT), also known as the GeneXpert test. Medical experts said the advantage of the test is that it is quick and portable – allowing teams to set up mobile testing centres or kiosks in containment zones instead of having to transport samples to laboratories. Since the swab samples are collected in a viral lysis buffer (solution), biosafety and biosecurity requirements to use TrueNat machines are minimal.

TrueNat machines were previously used to detect the Nipah virus during the 2018 outbreak in Kerala. “Both the tests [CB-NAAT and TrueNat] are cheaper than the traditional RT-PCR tests. Unlike CB-NAAT, TrueNat runs on a battery and doesn’t need an uninterrupted power supply and air conditioning. So, it can be carried to containment zones and slums for testing,” said Suresh Kakani, additional commissioner, Brihanmumbai Municipal Corporation (BMC).

With the goal of speedy detection of Covid-19 cases, the state government is planning to conduct TrueNat tests in medical emergencies like accidents or pregnancies. “We have instructed hospitals with the machines to run diagnosis in emergency cases along with the general screening of suspected Covid-19 patients,” said a senior official from the health department. As per sources, hospitals have also been instructed to conduct TrueNat tests on dead bodies in case doctors suspect Covid-19 infection.

In the absence of a vaccine or drugs to treat Covid-19, faster diagnosis and early medical intervention are essential. “Under the present testing procedure, diagnosis takes almost eight hours. This test [TrueNat] can provide faster results [20 minutes], saving more time and lives. However, we need more studies to understand its accuracy in the diagnosis of Covid-19,” said Dr Ramraje Nagsen, pulmonologist at JJ Hospital.

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