Since 20 March, India expanded its testing strategy to include all hospitalized severe acute respiratory illness (SARI) patients. Health minister Harsh Vardhan said the testing capacity has increased to 100,000 samples per day.

India has done 17,62,840 tests so far, with 86,191 samples tested on Monday across 347 public and 137 private labs.

“We are testing all hospitalised SARI and ILI (influenza-like-illness) cases, but we need to ramp up testing in non-affected covid-19 areas as well. We are gradually increasing though positive cases are in lesser numbers in these areas,” said Dr Randeep Guleria, director, AIIMS, and a member of the covid-19 empowered committee on disease surveillance and testing.

A WHO-China joint mission report released on 28 February said humans have no pre-existing immunity to covid-19, a newly identified pathogen. “Based on the epidemiologic characteristics observed so far in China, everyone is assumed to be susceptible, although there may be risk factors increasing susceptibility to infection. This requires further study, as well as to know whether there is neutralising immunity after infection.”

WHO said the highest level of national response management protocols must be immediately activated to contain covid-19 with “non-pharmaceutical” public health measures. “Immediately expand surveillance to detect covid-19 transmission chains, by testing all patients with atypical pneumonias, conducting screening in some patients with upper respiratory illnesses and/or recent covid-19 exposure,” the report had said. Back then, India had just four cases of covid-19.

The Centre is now ramping up the surveillance for SARI/ILI cases in covid- affected and non-affected districts, and will take help from medical colleges, if they are present there.

“Such measures will help to indicate the presence of any possible hidden infection at an early stage, thus helping in its timely containment,” said Vardhan.

Besides, community-based sero-surveys to estimate the prevalence of SARS-CoV-2 infection in the Indian population will also be conducted.

The surveys will involve collection of venous blood samples from 400 randomly selected individuals (one per household) from 10 clusters in each district. Samples will be tested for IgG antibodies using the ELISA test developed by ICMR-National Institute of Virology (NIV), Pune.

Coordinated by ICMR’s National Institute of Epidemiology (NIE) and National Institute of Research in Tuberculosis (NIRT), Chennai, they will cover 24,000 adults distributed equally across four strata of districts categorized on the basis of reported cases of covid-19. The surveys will be conducted in randomly selected 69 districts from 21 states.

“The results of the survey will provide information about the spread of SARS-CoV-2 infection in different parts of the country. Besides this community-based survey, the Union health ministry is also initiating hospital-based surveillance to monitor the trend of infection in all districts,” the government ICMR said.

“If covid-19 is not circulating in a given area, still adequate surveillance is required. A surge in SARI or ILI observed through clinical surveillance can be a sign of unrecognized covid-19 circulation in the general population and should prompt specific testing for covid-19,” said Dr. Sai Kiran Chaudhari, head of pulmonology department at Delhi Heart & Lung Institute.

“It is important to stress that not having laboratory-confirmed cases does not imply that an area is free from covid-19, and can be a sign of inadequate surveillance and may miss patients with active infection,” he said.