"Italy has predominantly been testing people with symptoms of a coronavirus infection, while South Korea has been testing basically everyone since the outbreak had become apparent," Backhaus says.

"Consequently, South Korea has detected more asymptomatic, but positive cases of coronavirus than Italy, in particular among young people."

The graph suggests that although younger people may feel fine they are in fact contagious.

"The surprisingly high number of tourists that have been diagnosed with coronavirus after returning from trips to Northern Italy suggests that the unnoticed and asymptomatic spread of the virus has probably been going on there for quite some time, building up to then ravage the elderly," Backhaus says.

He says COVID-19 hit the two countries "very differently" in terms of age even though the outbreak reached them both at around the same time.

He believes that if the virus spreads mainly among young people, then there is no risk to hospitals becoming overwhelmed with patients. But if it spreads to the older population, a hospital collapse "is looming".

Backhaus' post was shared widely online and one Twitter user called it "absolutely terrifying" that young people could be unknowingly spreading the disease.