SINGAPORE - About 100 migrant workers in dormitories previously cleared of the virus have tested positive for Covid-19 during routine biweekly testing.

The Ministry of Manpower and the Ministry of Health said on Tuesday (Aug 18) that the Rostered Routine Testing is for migrant workers living in dormitories, those working on construction or production sites, and those in the construction, marine and process sectors.

Over 100,000 migrant workers have begun the routine testing, done every two weeks.

Of the infections found in dormitories previously free of cases, the ministries said: "Some of these workers have resumed working.

"We have taken timely actions to contain and isolate the Covid-19 positive cases. We have also taken aggressive actions to contain, trace and isolate the close contacts."

It added that more than 60 per cent of the workers have recovered, and the measures taken have resulted in "effective containment" with few additional cases detected.

Out of about 7,000 migrant workers quarantined because of the 100 new cases, less than 2 per cent were subsequently found to be Covid-19 positive. "These are being managed according to strict protocols," the ministries said.

With the responsibility falling on employers to schedule their migrant workers for routine testing, seven in 10 employers to date have begun to do so through the online swab registration system.

There are currently about 18,600 workers overall who are still serving quarantines.

These include the latest group of 800 workers who were quarantined because a case was discovered among them in a cleared dormitory, which was reported last Wednesday.

The two ministries said the inter-agency task force is taking a "measured approach" with these 800 workers, with immediate close contacts of the infected worker being conveyed to a dedicated quarantine facility. The other residents of the dormitory block are also in quarantine as they await testing.

When new cases are detected on a cleared site, the entire block will be "promptly quarantined" as a precautionary measure, and all the workers swiftly tested, the ministries noted.

"We will rescind the quarantine subsequently for workers who are assessed to be not at risk. While this approach could affect up to a few hundred migrant workers for each case, it ensures that we contain the detected case and minimise spreading that could end up affecting thousands others."

The new infection cases in cleared dormitories and temporary sites are reminders of the need to be vigilant, they added.

The impact of safe distancing measures and segregation measures will be better assessed with more real life data gathered.

"This will help us assess patterns in the spread of infections, and review the extent of quarantine required to contain a detected case. Our priority will be to prevent and arrest new infections through early detection, timely containment and effective isolation."