Two days of falling infections raised hopes that were soon dashed.

From 1,037 new cases on April 23, the numbers dipped sharply to 897 and then 618 over the following two days. Just when Singaporeans were hoping the worst might be over, the number of new Covid-19 cases jumped to 931 on Sunday, while 799 new cases were announced yesterday.

One reason for the fluctuating numbers is that all workers in dormitories with symptoms are immediately isolated and treated.

That is especially true of dorms with high infection rates, explained Health Minister Gan Kim Yong. Testing can come later and the chances are high that they do have the disease. And when they are eventually tested and most likely found infected, they add to the daily count.

Indeed, the high numbers of cases in the dorms in recent weeks have been precisely because of Singapore's "aggressive" and "strategic" testing, and this continues.

Giving a different take on the numbers, Mr Lawrence Wong, Minister for National Development and co-chair of the multi-ministry task force, said the circuit breaker measures are working as the number of cases in the community has been going down.

The measure of success is not the hundreds of new cases identified daily - mostly foreign workers in dormitories - but in the number of cases in the community.

While these are not as low as hoped for, they are gradually falling, and point to one infected person infecting less than one other person. On Sunday, there were 43 such new cases - 18 among residents and employment pass holders, and 25 involving work permit holders who do not live in dormitories.

The Ministry of Health (MOH) recently split the cases of non-dormitory infection into the two groups when reporting the local figures:

• Singaporeans, permanent residents and foreigners on an employment pass.

• Foreign work permit holders not living in dormitories.

Both these numbers are important when looking at whether there is spread in the community.

The first is obvious and there can be no debate about why it is necessary to contain the spread before Singapore can breathe free.

The second group is smaller but equally important as it includes domestic workers living with local families, as well as workers living in Housing Board flats and shophouses.

But a large number are workers in the construction sector, said Mr Wong, who may interact more among themselves. There is a different strategy in keeping infections among them low, including having them stay home.

Mr Gan added that splitting these cases into the two groups helps the authorities to "better understand the way the virus transmits, the epidemiology behind it".

"Some foreign workers who are living in the community may not have family members, so their infection could be from the workplace."

Residents, on the other hand, usually live with family, so transmission could occur among family members.

The unlinked cases remain a worry as it means that someone with the disease has not been identified. Mr Gan said such cases need to be reduced to as low as possible.

On Sunday, there were 25 unlinked cases in the community - 10 among residents and 15 work permit holders.

Then there are the vast majority of new cases which are occurring among foreign workers living in dormitories.

They can almost be viewed as a separate outbreak as they have been isolated from the rest of society. Those still working because they are in essential services have mostly been moved out of dormitories, and are given priority testing and isolated if they have Covid-19.

All dorm workers have been isolated. This means the virus has been contained within this group.

At least for now, the exact numbers of those getting infected each day are not of critical importance in terms of policy decisions, as all non-essential work has been put on hold.

But those numbers will become important when Singapore wants to ease the current measures - and these dormitory workers start working again.

This is because, unless infections have been sharply checked or rooted out among this group of foreign workers by the time the circuit breaker measures are lifted, anyone mildly infected and not identified could pass the infection to the rest of the population once it is business as usual - unless these workers continue to be isolated.

As to when the current measures will likely ease, Mr Wong said that will happen when the number of new cases in the community can be contained to a single-digit number over a period of time.

He said: "When that happens, we will gradually start easing up measures and resuming activities."

This has to be done carefully and in a calibrated manner, as the risk of infection may come back. Then the priority will be rapid diagnosis and contact tracing to quickly ring-fence close contacts to prevent it from getting out into the community.