Eight out of 10 of Singapore's imported cases of Covid-19 have come in the last 10 days, a sharp spike signalling how the coronavirus outbreak is in a pandemic phase, with infections now coming from multiple countries.
As numbers here remained firmly in the double digits yesterday, experts warned they could keep rising for at least the next two weeks as travellers return following lockdowns around the world, before hopefully stabilising.
Of the Republic's 159 imported infections, 126 have been reported since March 10. This means, given the total of 345 confirmed coronavirus infections, nearly one in two was imported from somewhere else.
Of the 159 imported cases, 122 had a travel history to Europe, The Straits Times (ST) found.
"Since mid-March, Europe has been the new epicentre. Travel connections to Europe and the US are very strong, and it does not come as a surprise that there will be more exportations from Europe," said infectious disease expert Annelies Wilder-Smith, a visiting professor at Nanyang Technological University's Lee Kong Chian School of Medicine.
Of the 30 countries imported patients had been to, the United Kingdom led the tally with 36 patients reporting a travel history there, followed by the United States with 30, and China with 24. All imported cases from China had a travel history to Wuhan.
Experts and the Health Ministry warn that there will be more imported cases in the coming weeks as Singapore residents return home.
"We will continue to see this and perhaps an even larger number of cases over the next couple of weeks with many returning travellers, especially with the exponential rise in Covid-19 numbers in Europe, US and parts of Asia," Associate Professor Hsu Li Yang, who leads National University of Singapore's infectious diseases programme and is its co-director of global health, told ST.
"It will take a couple of weeks before the imported cases start to fall - given the incubation period of the virus and before the travel restrictions dampen the wave of imported cases to Singapore."
Infectious diseases expert Leong Hoe Nam said imported cases were inevitable as it would be difficult to seek out and quarantine every case of infection in Europe. "The reported numbers there do not necessarily reflect the current pandemic, and the number of infections is possibly 10 times more," he noted.
The coronavirus outbreak in Singapore, which began with the first imported case on Jan 23, has had three discernible phases so far:
• Wuhan phase: The first wave of cases was entirely from Wuhan, until Feb 4, when the first locally transmitted case was reported.
• Community phase: Thereafter, most infections came from community spread, many of them through clusters. The largest cluster was from a dinner at Safra Jurong, with 47 cases. Between Feb 4 and March 9, 127 confirmed cases were locally transmitted and just 15 were imported, as Hubei province went into lockdown.
• Imported phase: With the virus now spreading fast in many countries, imported cases are currently outpacing local transmissions, with 126 imported cases since March 10, compared with 59 local transmissions in the same period.
The trajectory here is a microcosm of the global spread, Prof Hsu said.
"The first phase was only natural, given the sharp jump in cases from China. Now we see the pandemic progress globally, and it is only natural to see imported cases from the rest of the world," he said.
Importations will continue as it is difficult to close down travel altogether, said infectious diseases expert Gregory Poland, head of vaccine research at the Mayo Clinic in Rochester, Minnesota, in the US. "When the number of cases seems to be stabilising, people start to travel and relax their restrictions and precautions, and this could spark transmissions again," he noted.
At the same time, however, countries have to keep a close watch on local transmissions.
"We still have to keep practising social distancing and proper hygiene as these cases are merely the tip of the iceberg. Even if the borders are sealed, local community transmission is still likely to happen, so we have to remove this opportunity," said Dr Poland.
National Development Minister Lawrence Wong on Wednesday announced that Singaporeans and residents returning to the country will all have to serve a 14-day stay-home notice, while travel overseas should be deferred.
"The point is that we must go beyond the headline number," he said, noting that as the vast majority of new cases will be returning residents who have to go into isolation, the problem can be dealt with.
But if the numbers continue to rise because of new infection clusters, despite best efforts at contact tracing to contain their spread, this could be a bigger cause for alarm, Mr Wong said.
"This will then suggest that the virus is transmitting itself in a self-sustaining way," he noted.
Urging vigilance, experts said Singapore could enter a new phase of community spread after the number of imported cases has subsided.
"Those who are on leave of absence or stay-home notice might spread it to their family even if they don't go out," said Dr Leong. "It is also unlikely that the cases will drop to zero as Singapore is not in a lockdown situation, and those who are very mildly symptomatic might still spread the virus without realising it."
"But it'll likely be a mild increase if precautions are followed," added Dr Leong.
Experts said Singapore should continue its efforts to flatten the curve, practising social distancing to slow the spread of the virus in the community so the healthcare system is not overwhelmed. This will also keep mortality low.
Singapore has not yet had a death from Covid-19.
"Singapore has done extremely well over the past two months. Despite a high number of importations, especially early on in the outbreak from China, Singapore's curve has remained sufficiently flat," Prof Wilder-Smith said. She attributed this to the country's rigorous interventions, and the willingness of the public to adhere to social distancing and temperature screening.
A flatter curve will also buy time, with the Government announcing plans on Wednesday to convert normal hospital wards into isolation wards, and quarantine facilities possibly into care centres for Covid-19 patients with less severe symptoms, if the number of cases continues to rise.