About 800 migrant workers have been quarantined after a case of Covid-19 was discovered in a dormitory that had been cleared, Singapore’s Ministry of Health said in a statement.

Singapore earlier this week said it was “actively monitoring the dormitories to manage the risk of new outbreaks,” as there had been instances where new cases were discovered at previously-cleared dorms.

The discoveries could mark a setback for the country that this week said all its workers’ dorms have been cleared of infections. This paves the way for the majority of these laborers to return to work by the end of the month. Migrant workers, who live in cramped quarters, have accounted for the vast bulk of Singapore’s confirmed Covid-19 cases, sparking questions about how the wealthy city-state treats these low-paid foreigners.

Singapore is cautiously reopening after locking down most activities in a two-month “circuit breaker” designed to halt the spread of the virus. Schools have reopened, masks are mandatory, and restaurants are back to business. Yet life isn’t fully back to normal -- gatherings are generally limited to five people, large events have been canceled and international travel restrictions mean Singapore’s jewel of an airport is largely empty.