Of the 13 pre-school staff who tested positive, 11 are old infections

Thirteen pre-school staff have tested positive for Covid-19 since active screening for that group began this month, said the Health Ministry yesterday.

However, subsequent testing showed that 11 of these were old infections and the staff had recovered - meaning they were no longer infectious, said the ministry's director of medical services Kenneth Mak during a virtual press conference.

Results of the serology test, which detects antibodies to tell if a person has been infected, are pending for two staff.

Patients have antibodies around two weeks after they recover from the infection and will not have them at the point of infection.

More than 39,000 pre-school staff have been tested for the coronavirus so far. Of these, 13 staff - about 0.033 per cent - have tested positive.

All pre-school staff have to undergo a one-time swab test for Covid-19 as a precautionary measure before the centres reopen next month.

"The results of the serology tests, together with the polymerase chain reaction tests that we performed, were then critically evaluated. The evidence suggests that these are not active, fresh infections, but old infections," Associate Professor Mak said.

"The test results suggest that these staff members have all recovered from the infection. As a result, it is our evaluation... that none of these staff members is currently a risk to either other colleagues within the pre-school setting, or to the children who are supported and cared for by pre-school staff. And this, of course, means that they are not infectious."

He said the authorities are unable to say for sure when these people had been infected. The majority of the staff were asymptomatic.

"It reaffirms our assessment that previously, prior to the circuit breaker, there was some level of community spread. But with the circuit breaker in place, we've seen the number of community active cases coming down very significantly, consistent with our assessment that the circuit breaker has been effective."

The country's circuit breaker measures will be eased in three phases from next Tuesday.