SINGAPORE - "We seem to have two separate epidemics ongoing," said Associate Professor Alex Cook. "The massive outbreak in the dorms and a relatively controlled outbreak in the rest of society."

Prof Cook, vice-dean of research at the NUS Saw Swee Hock School of Public Health, said that while there is potential for the outbreak to "spill over from the dormitories to the community", the risk is low while circuit breaker measures are in force.

He added: "The number of cases in the dorms is emotionally shocking, but is quite in line with the projections based on the last few weeks of cases: We're seeing doubling in the number of cases every two to three days."

There were 1,111 new Covid-19 cases on Tuesday (April 21), the vast majority of whom are work permit holders residing in foreign worker dormitories. The Ministry of Health said 20 of the cases are Singaporeans or permanent residents.

The disease is in the exponential growth stage in dormitories, said Prof Cook. "So the daily case counts will keep accelerating unless we can substantially reduce contacts between infected and susceptible men in the dormitories."

His colleague at the school, Associate Professor Hsu Liyang, who is both an infectious diseases expert and an epidemiologist, predicts that the number of new infections among foreign workers living in dormitories will stay high for several more days.

He said: "What we are seeing in the dorms reflects events from about five days ago, given the interval period of the virus."

Like Prof Cook, he said that while measures are in place, including isolation areas in dormitories, spread of the virus from the dormitories to the rest of the community will be very minimal.

But he added: "However, if the outbreak among the foreign workers is not contained, easing circuit breaker restrictions will increase the risk of the spread of the virus."

He said in theory, measures could be eased for the rest of the country while remaining tight for foreign workers, but doing so "does not convey an impression of solidarity as a country".

Furthermore, the number of new cases in the community - which has not fallen below 20 cases a day since the measures had been implemented, is still quite high.

Said Prof Hsu: "Circuit breaker restrictions should probably be eased only when we are sure that the community spread has been contained - that is, when the case count has been in single digits for at least a couple of weeks."

Prof Cook added that the dormitory outbreak does pose risk for the rest of the population, in terms other than risk of virus spread.

"While they're separate outbreaks from the point of view of transmission, they are not when it comes to treatment.

"If we keep having a thousand or more cases a day, it will impose a massive strain upon our healthcare system," he said.

Public hospitals here have postponed non-urgent cases since January to free up hospital beds for patients infected with the coronavirus.

Prof Cook added: "It therefore behoves us to adhere even more strictly to the physical distancing measures in place, because each new infection adds extra stress to the healthcare system."