SINGAPORE - In a "utopian situation" with an infinite supply of masks, everyone wearing one regardless of their health status will help contain the coronavirus swiftly.

But as this is not possible, and given the Covid-19 outbreak is a "marathon", healthy people under the age of 60 should not wear masks on a daily basis, infectious diseases expert Leong Hoe Nam told The Straits Times on Wednesday (April 1).

The day before, The New York Times reported that the United States' Centres for Disease Control and Prevention (CDC) was reviewing its guidelines on who should wear masks.

On Monday, Austria made the wearing of masks in supermarkets mandatory in a bid to stem the spread of the virus. The Czech Republic went a step further, making mask-wearing mandatory outside of the house.

Readers had also written in to ST asking that people be advised to wear masks despite not showing symptoms.

At a media conference on Tuesday, the Health Ministry's director of medical services, Associate Professor Kenneth Mak, said the ministry was looking at evidence "very carefully" and conducting a review of its stance on masks, as it does with its other policies.

"As far as masks are concerned, we are in fact in the process of continuing to review the data that's available, both in the literature as well as the international experience," he said.

He added that recommendations would be made after the review is completed.

Dr Leong, who practises at Mount Elizabeth Novena Hospital, said on Wednesday the need for everybody to wear a mask regardless of their health might eventually be a requirement if Singapore is unable to control the spread of the virus here.

But, he noted, masks are still in short supply around the world.

"I think it's a moot point to get people to wear masks when they're still in scarcity. It's like telling the poor, the way to get out of poverty is to get more money - but I don't tell you how to get that money," he said.

"The mask situation has improved, but we're not seeing endless supplies of masks. If all of us had to mask up today for one week, we might finish all our stock of masks immediately.

"The real science of it is, if everyone maintains their 2m distance, watches their hand hygiene, doesn't go out when they're sick, then we may not even need the mask. By keeping 2m away, I would have done what the mask can do," he added.

Those older than 60 can use a mask when they go outdoors as they are more vulnerable, he said, adding that they also have to bear in mind the need to conserve their own supply of masks as the outbreak may last for another six to nine months.

Infectious diseases expert Paul Tambyah from the NUS Yong Loo Lin School of Medicine said at the moment, data on mask use is not entirely clear.

He noted that new data suggests the receptor for the virus which causes the Covid-19 disease may be present in the nose and not just in the lungs.

"If this is confirmed, then (using) something which covers our noses may turn out to be important," he said, adding that more information would likely be available in a week or so.

Dr Wong Tien Hua, family physician at Mutual Healthcare Medical Clinic, said there is a need for "situational usage" of masks at the moment.

"On the bus, on the MRT... when you're queuing up or in a crowded place, wearing a mask is the smart thing to do," he said.

He noted, however, that Singapore has taken a multi-pronged approach to fight the virus, including using social distancing measures and closing down entertainment outlets.

"If you tell everybody to wear masks, it's kind of missing the point because we have other measures," he said.

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Another family physician, Dr Leong Choon Kit of Mission Medical Clinic, felt that getting everyone to a mask up might backfire.

"If mass wearing of masks is advised, the cost of masks will rise again and the public will buy them from unreliable sources. If they are of dubious quality, they will not serve their function. So it will end up as a futile attempt to control the virus," he said.

There is no need for a blanket call to mask up unless there is more community spread here, he added.

A growing number of people online had also called for people to make their own face masks from improvised materials.

Dr Leong Hoe Nam noted that cloth masks have proven to be less effective than proper surgical masks. However, he added: "But I believe it confers some advantage rather than none, so if I couldn't get a decent surgical mask, I'd use at least a cloth mask."

Dr Wong said: "Wearing any kind of barrier is better than no barrier, especially for those who are talking or sneezing."

But Prof Tambyah and Dr Leong Choong Kit disagree.

"Wearing an ineffective mask is far worse than not wearing one," said Dr Leong.

"If I do not have a mask at all, I will consciously avoid certain places, but if I were to wear one, I may be less conscious and put myself at risk."

Prof Tambyah said very few studies had tested different types of masks in clinical settings, and he did not know of any that involved patients coughing or sneezing.

"I don't think we should be specifically encouraging people to make their own masks, until there is good objective data on how effective such masks are under clinical conditions," he added.

No data exist yet that suggest asymptomatic transmission should be a concern, said the infectious disease experts.

Prof Tambyah said that while epidemiological data may suggest that people could be infectious the day before their onset of symptoms, more detailed molecular evidence had not yet been publicised on these cases.

Dr Leong Hoe Nam said that while asymptomatic cases of transmission may exist, they play a "very, very small" role in the transmission of the virus.

"If the epidemic were driven by many asymptomatic transmitters, the Chinese authorities wouldn't have been able to control it so quickly," he added.