Visitors wearing face masks walk along the Jubilee Bridge in Singapore on Feb 17, 2020. (ROSLAN RAHMAN / AFP)

More cases of coronavirus infections are emerging in Singapore with no known source of transmission. So far, of the 50 local cases, a quarter cannot be accounted for.

The numbers are still relatively small, and contact tracers are working hard to find out how the patients had been exposed to the virus.

If they succeed in identifying the sources and ring-fencing other people who might have been exposed to the virus, then the current containment measures are still working fine.

Even if they cannot identify the source of infection, but are able to prevent its further spread, the disease remains contained.

But what if they cannot, and more such cases emerge in the coming days and weeks? That is when Singapore will need to take a hard look at all information available from around the world and decide on its next step.

The best scenario would be, of course, if the virus has mutated and becomes both less transmissible and has no, or a very low, mortality rate. If that were to happen, the whole world could breathe a collective sigh of relief and relax the measures now in place.

Social distancing is already happening to some extent now, as some companies have activated business contingency plans such as having staff work from home

Unfortunately, this appears to be the least likely to happen.

Dr Sebastian Maurer-Stroh, deputy executive director of A*Star's Bioinformatics Institute, said that the 73 full genomes of the virus from patients around the world that have been shared show very little variation.

So the virus does not appear to be getting less virulent with each generation, as often happens.

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The Ministry of Health (MOH) said it was carefully monitoring the situation, and keeping a close eye on several "triggers" that could presage a change of its stance - either to introduce more measures, or to relax some existing ones. These triggers include:

• How severe or mild the infection is. In Singapore, about 15 percent of patients to date have ended up severely ill and requiring intensive care.

• How easily transmissible it is. From current data, one person goes on to infect two or three more people.

• The number of people infected here. So far, 50 people have been infected locally.

• The mortality rate. This now stands at 2.9 percent in China - the epicentre of the epidemic - and 0.4 percent in the rest of the world, but these figures are subject to daily changes.

WORST-CASE SCENARIO

If uncontrolled, the virus could infect 60 percent of any given population, experts in Hong Kong said.

Explaining this projection, Professor Teo Yik Ying, dean of the NUS Saw Swee Hock School of Public Health, said this is based on the current transmission number of two to three people.

"However, this can change according to the public health measures that are adopted to reduce the risk of spread," he said.

Associate Professor Alex Cook, vice-dean for research at the school, said that in the early stages of the spread of a new virus, the population is "naive", as none has had the infection before.

If we can bring the infection rate down to 10 percent, that will save many lives. We don't know if it's possible to get it so low, but we can try - by taking care to isolate yourself when sick and observing good hygiene practices.

Alex Cook, Vice-dean for research, NUS Saw Swee Hock School of Public Health, Singapore

But as it continues to spread, some people may get infected but develop mild symptoms. They can develop immunity to the virus and so break the chain, as they won't pass it on to anyone else.

"Increasingly those contacts become 'wasted' from the virus' perspective, and more and more cases don't infect anyone," he said.

However, an infection rate of 60 percent is a large number. Given Singapore's population of five million, that's three million people who could get infected.

If 60 percent of people here get infected and 2.9 percent die - going by China's figures - that's 87,000 people. While this is the worst-case scenario, it is highly unlikely to pan out.

Outside China, the mortality rate runs at 0.4 percent - that immediately drops the number of probable deaths, should 60 percent of the population in Singapore get infected, to 12,000 people.

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But that is still way too high. On average, about 21,000 people here die each year - so that would push up deaths by more than 50 percent.

Furthermore, the mortality rate outside China is based on two deaths out of 505 confirmed cases. Another death outside China could push up that rate.

"If we can bring the infection rate down to 10 percent, that will save many lives. We don't know if it's possible to get it so low, but we can try - by taking care to isolate yourself when sick and observing good hygiene practices," Cook said.

"Complacency is what we need to guard against because that is what will lead to spread to others," he added

MITIGATION

So what can Singapore do to bring the number of infections and deaths to as low a number as possible?

The multi-ministerial task force has introduced various measures to reduce the risk of coronavirus transmission in the country.

It started with temperature screening at the airport for passengers arriving from Wuhan on Jan 3, followed by a ban of all travellers from the epidemic's Chinese epicentre, Wuhan, and those holding Hubei passports.

Since then, measures have been gradually stepped up, including raising the disease response level to orange - just one level below red, which is the highest - on Feb 7 when local transmission with no known links occurred, so Singapore can more aggressively try to contain the spread of the virus.

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With that move, the Education Ministry cancelled all inter-school events and external activities till the end of the March holidays; companies were encouraged to implement business contingency plans; visits to pre-schools and eldercare services were restricted; and mass events were discouraged, with temperature screenings in place if they go on.

If too many new cases of unknown origins continue occurring and the virus continues to be as virulent, Singapore will need to move from containment to mitigation. Cook said moving to mitigation means "we accept we cannot stop the outbreak, and instead the aim is to minimize the impact".

What Singapore is striving to do now, said Alex Cook, is to find and contain cases so they do not become clusters. If there are clusters, the point is to prevent them from fragmenting into even bigger clusters

Measures then would include social distancing so there is less mingling among people here, to reduce the risk of transmission.

When that occurred during the severe acute respiratory syndrome (SARS) outbreak in 2003, schools and childcare centres were closed.

Social distancing is already happening to some extent now, as some companies have activated business contingency plans such as having staff work from home.

This not only reduces the risk of several employees getting infected, but also reduces crowds on public transport.

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Associate Professor Hsu Liyang, the Infectious Diseases Programme leader at the NUS Saw Swee Hock School of Public Health, said: "Mitigation is meant to reduce the speed of transmission.

"This does two things. First, it prevents the healthcare system (clinics and hospitals) from being overwhelmed, which will result in a rise in deaths not only from the virus, but also from all other causes.

"Second, if delayed sufficiently, there is a hope that an effective treatment or vaccine may become commercially available that may be able to prevent more deaths."

Vaccine development has been expedited and Britain has started testing a vaccine on animals. But it will be many months before it is ready for human use.

With the passing of winter in the northern hemisphere, there is hope that the viral transmission in China will abate, since the virus does not thrive in a hot and humid environment.

Even if the outbreak tapers off in China, Singapore should not let down its guard.

Associate Professor Kenneth Mak, Singapore's director of medical services, said that outbreaks in other countries generally peak about two months after doing so in the country of origin.

Would it be better for Singapore to implement social distancing immediately if that is more likely to work? The situation is not yet so dire. Putting in draconian measures now will impose unnecessary hardship on people.

What Singapore is striving to do now, said Cook, is to find and contain cases so they do not become clusters. If there are clusters, the point is to prevent them from fragmenting into even bigger clusters.

"These efforts now will buy us time to be better prepared and to have more knowledge on the severity of the virus, so we can gauge the correct response during the mitigation phase," he added.

One thing all the experts agree on: This is not something that will blow over in a week or two.

This may be a long battle, so more stringent measures should only be implemented when they will make the most impact.

Meanwhile, life has to go on, but it will not be life as normal - at least for some time.