A source from the Corporation said the Health Department has devised a ring-fencing plan to prevent spread of the mutated virus. “As per the SOP, we need to test only those who visited the city between December 9 and 23. However, the Department has directed us to test even those who came to the city after November 25,” the source said.

A total of 218 people arrived at Chennai airport 48 hours before the banning of flights from the UK and 1,791 people during the two weeks that immediately preceded the ban. In total, 2,805 had come to the city from the UK after November 25. The source explained that the move to test travellers who entered the State after November 25 and their primary contacts has been taken as a measure of caution.

“If the travellers were COVID positive, they would have recovered but they could have passed the virus on to their primary contacts,” he added.

The Chennai Corporation as well as other local bodies have been ordered to strictly home quarantine those returning from abroad even if their test results are negative. The returnees will be monitored by sanitary workers and Health Department staff. Fever surveillance will be done to check abnormal spurts of cases which could be the result of public, religious and cultural gatherings.

The Health Departments in western districts have begun to trace and test UK returnees to prevent spread of the muted virus. In Erode district, 16 people arrived from Britain since December 15. Six people who returned to Hosur were asked to be under isolation for two weeks and their health was being monitored.

In Coimbatore, four, including two women, who arrived from the UK on December 16 and 17 were tracked and tested again.