• A new study shows that carriers of novel coronavirus can spread the infections before the usual COVID-19 symptoms appear.
  • The study echoes earlier findings from late January when some officials said the virus might spread before the onset of symptoms. Those findings were disputed at the time.
  • Medical professionals should take into account the possibility of presymptomatic transmission when conducting contact tracing.
  • Visit BGR’s homepage for more stories.

Reports in late January said that the novel coronavirus was spreading before the onset of symptoms. That was a shocking development at the time. Back then, there were less than 3,000 confirmed cases, and most of them located in China. Less than a week later, nearly 25,000 cases were registered, but public officials were saying that virus transmission wasn’t possible before symptoms appear. Fast-forward to present-day, we have nearly one million cases in the world, and the death toll is pushing 50,000. And the CDC just published a study that says presymptomatic COVID-19 patients can spread the disease.


The new study looked at 243 cases of COVID-19 cases from Singapore that were reported from January 23rd to March 16th. The researchers observed seven clusters of cases where “presymptomatic transmission is the most likely explanation for the occurrence of secondary cases.”

Here are two examples of what presymptomatic transmission may look like:

Cluster A. A woman aged 55 years (patient A1) and a man aged 56 years (patient A2) were tourists from Wuhan, China, who arrived in Singapore on January 19. They visited a local church the same day and had symptom onset on January 22 (patient A1) and January 24 (patient A2). Three other persons, a man aged 53 years (patient A3), a woman aged 39 years (patient A4), and a woman aged 52 years (patient A5) attended the same church that day and subsequently developed symptoms on January 23, January 30, and February 3, respectively. Patient A5 occupied the same seat in the church that patients A1 and A2 had occupied earlier that day (captured by closed-circuit camera) (5). Investigations of other attendees did not reveal any other symptomatic persons who attended the church that day.

Cluster B. A woman aged 54 years (patient B1) attended a dinner event on February 15 where she was exposed to a patient with confirmed COVID-19. On February 24, patient B1 and a woman aged 63 years (patient B2) attended the same singing class. Two days later (February 26), patient B1 developed symptoms; patient B2 developed symptoms on February 29.

In other words, if you’re carrying the new SARS-CoV-2 virus, you might infect others well before showing any signs of the infection yourself.

We already knew that many COVID-19 patients will not even develop any symptoms, and their immune system would be able to beat the infection without any help. But these people are still contagious, and they’re able to spread the disease to others around them. That’s why it’s essential for most people to stay indoors for more extended periods, to decrease the risk of transmission. The new study indicates that all patients, no matter whether they will show COVID-19 symptoms or not, might infect others well before they suspect they have the illness.

The study warns medical professionals to account for the possibility of presymptomatic transmission while trying to trace the infection. “Public health officials conducting contact tracing should strongly consider including a period before symptom onset to account for the possibility of presymptomatic transmission,” the study notes.

The finding further reinforces the idea that strong social distancing measures should be enforced to limit the spread of the virus. The longer we stay indoors, the higher the chance of our immune system to kill the novel coronavirus. If you’re showing symptoms, you should contact your doctor and follow guidelines. Depending on how your COVID-19 case progresses, you might be told to stay at home under observation, or you might be taken to a hospital.

Chris Smith started writing about gadgets as a hobby, and before he knew it he was sharing his views on tech stuff with readers around the world. Whenever he's not writing about gadgets he miserably fails to stay away from them, although he desperately tries. But that's not necessarily a bad thing.