Coronavirus: study of Singapore and Tianjin outbreak says some Covid-19 infections linked to asymptomatic carriers

The early-stage Belgian-Dutch research suggests that almost half of those who caught the coronavirus in Singapore did so from someone not showing symptoms

A new study suggests about half of people who have caught Covid-19 in Singapore appeared to do so from others who were yet to show any symptoms.

The pre-print study, which has not been peer reviewed, analysed data from clusters in Singapore and Tianjin in China to work how the virus is transmitted and how long it takes people to develop signs of it.

In Singapore, 48 per cent of people on average, caught the virus from someone who had not started showing symptoms. In Tianjin, it was even more, at 62 per cent of people, according to the researchers in Belgium and the Netherlands.

On average, it took sufferers in Singapore five days to develop signs of the disease, compared to almost four days in Tianjin.

The study was posted on MedRxiv, a server for papers that have not yet been published.

The World Health Organisation’s emerging diseases and zoonoses unit recently said preliminary data showed patients shed more virus in the early stages of the illness, including before they start to show symptoms.

"That is something which is in observational data, and fairly well documented in multiple communities, not just in China," said Dr Ravi Arora, a specialist in internal medicine at NMC Speciality Hospital in Abu Dhabi.

"Asymptomatic transmission is something we were not expecting, not prepared for, but it seems to be happening. And it increases the spectre of the disease much more because practically anyone, even before they start coughing, is potentially a spreader of the bug. That again makes it a lot less containable and the spread highly imminent."

The US Centres for Disease Control and Prevention has said that "we are still learning how" Covid-19 spreads because it is a new disease.

"Some spread might be possible before people show symptoms; there have been reports of this occurring with this new coronavirus, but this is not thought to be the main way the virus spreads," according tot the CDC website.

Other preliminary research has also shown that the pathogen can survive in the air for up to three hours.

However, researchers said that even if aerosol transmission is possible, it is unlikely to be the main source driving the pandemic.

"The current scientific consensus is that most transmission via respiratory secretions happens in the form of large respiratory droplets ... rather than small aerosols," co-author Dylan Morris, a graduate student in the Department of Ecology and Evolutionary Biology at Princeton University, was quoted as saying by Live Science, a website which focuses on science news.