Patients with mild and moderate respiratory symptoms who are currently not screened for the novel coronavirus infection under the existing testing criteria could spread the virus, public health experts said on Tuesday, iterating their earlier call for expanded testing criteria.

As India’s coronavirus counts climbed overnight with 508 new patients and 13 more deaths to reach a total of 4,789 confirmed cases and 124 deaths, networks of physicians and community medicine experts said tests should be expanded to anyone with respiratory symptoms.

The Centre’s current testing criteria recommend looking for the coronavirus only in persons with a recent foreign travel history and their contacts, contacts of positive cases, and hospitalised patients with severe acute respiratory illness.

Multiple public health experts and virologists have since mid-March underscored the importance of widening the testing criteria to include persons who might have mild respiratory symptoms. Global studies suggest that around 80 per cent of infected persons have mild symptoms.

“The need to test everybody with symptoms, even mild symptoms, is extremely important,” said Thiagarajan Sundararaman, a community medicine specialist and a member of the Jan Swasthya Abhiyan (JSA), a nationwide network of physicians and health experts.

“At this time, patients with mild respiratory symptoms and severe symptoms or influenza-like illness but not in hospital go without diagnosis. They should be viewed as Covid-19 unless proven otherwise,” Sundararaman added. “That is the basic way to deal with epidemics.”

Sundararaman said there was anecdotal evidence that Covid-19-infected persons with mild symptoms had visited hospitals for other ailments and unknowingly exposed others to the risk of infection.

“A patient in Uttar Pradesh went to one clinic, then to a district hospital, then a medical college hospital. He must have come in contact with hundreds of persons,” Sundararaman said.

The Indian Council of Medical Research has helped expand the country’s testing capacity. Around 136 government laboratories and 50 private labs are now qualified and prepared to test for Covid-19.