NEW DELHI, India (AP) – In June, India began using cheaper, faster, but less accurate tests to scale up tests for the coronavirus – a strategy the United States is now considering.
These rapid tests have improved India’s test levels almost five times in two months. But government figures suggest that some parts of the country may have become too confident about the rapid tests, which could miss infections. Experts warn that safe use of them often requires rehearsals, something that does not always happen.
Falls went faster as labs were able to scale up tests once India’s hard lockdown was relaxed. So far, authorities have razed the use of the more accurate molecular tests that detect the genetic code of the virus. But on June 14, India decided to support this with faster tests that screen for antigens, such as viral proteins.
Although less accurate, these tests are inexpensive and give results in minutes. Most do not require a lab for processing or specialized equipment or trained personnel. The plan was to increase testing rapidly to identify infected people and prevent them from spreading the virus. Sample tests with both tests increased from 5.6 million mid-June to 26 million two months later, and nearly a third of all tests performed daily are now antigen tests, health officials say.
But India’s experience also highlights the inherent decline of over-reliance on antigen testing, at the expense of more accurate testing. The danger is that the tests can remove many fakes that are infected with COVID-19, and this contributes to new spread of the virus in severely affected areas.
Rapid test results can be backstopped with more accurate laboratory tests, but these are slower and more expensive. Experts also warn that since the two types of tests differ in accuracy, they need to be interpreted separately to properly assess the spread of infection – something India does not do.
The US faces a similar need to find a balance between speed and precision, with exaggerated labs struggling to keep up with the outbreak. Researchers at Harvard and elsewhere are proposing to develop a $ 1 saliva-based antigen test for all Americans to test themselves daily, something that has not yet been approved by the Food and Drug Administration.
Dr. Harvard’s Michael Mina says antigen tests do not catch as many patients early in the infection when virus levels are low. But these people are not considered the biggest threat to the spread of the disease, because it is only after the rise in virus levels that they become more infectious, and by the time they are picked up by antigen tests, he said. hy.
Because a negative antigen test does not guarantee that a person is virus free, people should be re-tested regularly, said Dr. Ashish Jha, director of Harvard’s Global Health Institute. “If their symptoms change, you want to think about re-testing these people.”
India’s strategy is different. Health officials have asked for those who tested negative with antigen tests but had symptoms to retest with the more accurate laboratory tests.
But India has for the most part been opaque about how many negatives were re-tested, and what type of tests were used.
The state of Delhi, which encompasses the Indian capital, New Delhi and where the Supreme Court controls tests, was one of the first to aggressively use antigenic tests to screen patients for free. Centers were created in dispensaries, schools and government offices. But only 0.5%, as 1,365 of more than 260,000 people who tested negative from June 18 to July 29, were retested, court documents show. Delhi conducted more than 280,000 tests during this period.
“That’s abysmally low,” said Drs. SP Kalantri, a public health specialist in Maharashtra, India’s worst hit state. He said the decline in the use of more accurate lab tests by almost half, from a capacity of 11,000 tests daily to just 5,400 tests per day, was a worrying trend
Under guidelines set by the World Health Organization, India would need to perform about 140 daily tests per million people to safely relax coronavirus infections.
Rajesh Bhushan, India’s top official, has repeatedly pointed to India’s cumulative total of the two types of testing to assess that India is testing more than the WHO standard. Authorities also use this to calculate the percentage of samples that test positive, which is an important metric for assessing test performance.
But Jha said that combined data from the two types of tests could not be used to conclude that infections are declining in India because the use of less accurate tests would automatically dispel the number of positive results.
Experts fear that too much reliance on antigen testing without re-testing could lead to efforts to contain the virus, as it spreads to states with fragile health care systems, such as Bihar and Uttar Pradesh, with a combined population of more than 300 million.
The two states now do more than 100,000 tests every day, most in India. But only a fraction – 6,100 in Bihar and 30,000 in Uttar Pradesh – use laboratory tests.
Jha said the antigen tests were a way to extend testing to people who did not have access to laboratory tests, but that did not mean that use of the more accurate tests would be reduced.
“I want both,” he said. The rapid test “is not a perfect replacement.”
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Perrone reported from Washington. Associated Press authors Biswajeet Banerjee in Lucknow, India, and Indrajit Singh in Patna, India, contributed to this report.
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The Associated Press Health and Science Department receives support from the Howard Hughes Medical Institute’s Department of Science Education. The AP is solely responsible for all content.
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