India is beginning to ramp up testing for Covid-19. The central government and several states have begun to procure lakhs of RT-PCR test kits to screen for the virus. Scores of government workers have fanned out across the country to track contacts of people who have tested positive. Moreover, India is considering novel testing protocols in order to increase the population that can be covered with the tests it already has.

However, India still lags behind several countries, with a testing rate of just over 200 per million persons, though some states are significantly higher. In this context, the health ministry’s recent announcement that there is no community transmission in India needs to be investigated further.

Despite occasional stories of individuals who have reported going to a hospital with Covid-19 but had no travel history, two official studies conducted have found no positive cases from the community. Consistent with guidelines from the World Health Organization (WHO), the Ministry of Health announced after the second of these studies—which found only 40 positive cases among people with no relevant travel history, out of 5,911 patients with severe acute respiratory illness—that Covid-19 had not spread through the community.

While this is comforting news, it is prone to misinterpretation. The problem these studies face is that, with low rates of testing, there is a high chance of not finding Covid-19 in the community even if it is there. By our statistical calculations, even if nearly 0.01% of the community were infected, there would be a greater than even chance that these two studies of non-travellers would yield no confirmed cases.

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