COVID-19 'patient zero' may remain an unsolved mystery

Three months after the first known cases of COVID-19 emerged, there is still no clear-cut answer as to who "patient zero" is, or where it came from.

Also known as the index case, patient zero refers to the first human infected in an outbreak.

As of Wednesday, COVID-19 has spread to more than 196 countries, killing more than 16,000 people worldwide.

Tracking down patient zero could be key to understanding the novel virus behind the ongoing global health crisis and how to curb further transmission. But in many hard-hit countries, no one knows how the virus got there or who contracted it first.

The search for patient zero in each affected country has proven a herculean task. This is largely due to the long incubation period and asymptomatic transmission of COVID-19. Infected individuals who are not showing symptoms can cruise through screenings at ports of entry undetected and infect others unknowingly, making the route of transmission hard to trace in most cases.

Here's what we have learned so far about the first patients in four countries according to scientists and various media reports.

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