Questionable testing belies drop in India's Covid-19 infections

By Muneeza Naqvi and Chris Kay

India’s daily coronavirus infections have been cut in half since a peak of more than 97,000 in mid-September, but the significant drop has raised fresh questions over the nation’s testing regime and whether it reflects the true state of its epidemic.

As the country on Thursday surpassed the grim milestone of 9 million total infections, the official daily numbers appear to show a marked slowdown in the spread of the disease. Once poised to overtake the US as the nation with the highest caseload, India for weeks has been reporting fewer than 50,000 new cases a day, while infections are skyrocketing across America.

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Rather than showing India is gaining control over Covid-19, the slowing momentum may largely reflect spotty testing levels and a heavy reliance on questionable kits.

Daily testing in the country of 1.4 billion people has picked up since the early days of the pandemic -- currently at about 1 million -- but it’s still much lower than most countries with high infections. Just as significant, nearly half come from less-reliable quick antigen tests, which can report false negatives as much as 50% of the time.

The result is that India’s Covid-19 cases are likely much higher than the national numbers. Health experts fear new infection waves as the country gathers to celebrate a season of weddings and Hindu festivals amid a smoggy winter in the densely populated north.

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Rapid antigen tests “are not very reliable, not sensitive and the patients are not getting treatment at all,” said Harjit Singh Bhatti, president of the Progressive Medicos & Scientists Forum who has been working on the front lines in a suburban Delhi hospital since the epidemic began. “The coming months will be very dangerous.”

Most other countries with big outbreaks, such as the US and UK, use RT-PCR tests that take longer to generate more reliable results by detecting the genetic material of the virus. Experts say rapid antigen tests can help countries with surging outbreaks quickly detect where the worst hit areas are. But for an accurate understanding of the spread these should be followed up by RT-PCR tests.

False negatives

“Rapid antigen tests can have very high false negative rates -- you’re supposed to follow up with RT-PCR, which is almost not done” in India, said T. Sundararaman, a New Delhi-based global coordinator of the People’s Health Movement.

As of last week, 49% of India’s daily tests were rapid antigen -- up from about 25% to 30% in mid-August, according to the most recent federal data. Yet some of the country’s most populous states don’t regularly publish detailed testing data. That makes it hard to pinpoint the worst affected areas or assess their testing strategy.

“How many cases you can identify depends on how effective your testing is,” said Rijo M. John, an adjunct professor at Rajagiri College of Social Sciences in Kochi. “We do have reasonably good data on tests and cases in city centres and more urban districts, but a similar kind of data is missing in rural areas.”

Bihar, an eastern state with a population of over 100 million, may turn out to be the most vivid example of how low overall testing and even lower high-quality tests could be obstructing a clear picture of India’s pandemic. As many as 88% of all tests in the impoverished state are the rapid antigen variety. It also held an election this month, India’s first major vote since Covid-19 struck. Hundreds of thousands of people crowded together at campaign rallies, with few wearing masks.

Any potential spike has so far been muted in official data. On Thursday, Bihar added only 604 new infections over the previous day, despite its huge population. Uttar Pradesh, India’s most populous state with over 220 million people, more than twice as many as Bihar, reported over 2,500 new cases.

In comparison, New Delhi, with an estimated 16.8 million people, added more than 6,900 new infections. It publishes testing numbers every day, including information about the kind of tests used. Still, its regime -- tilted heavily in favor of rapid antigen tests -- has come under criticism over the last two weeks when new cases have soared amid cooler temperatures, high pollution and poor social distancing.

With hospitals in Delhi filling up again, some health experts believe the situation will only be worsened by unreliable testing.

“We are clutching at straws,” said Sundararaman.