It’s interesting, scientists are saying they don’t have enough info, but there is two strains, so indistinct they aren’t even sure if they should be called different strains, but being classified as the L type and the S type. They think the S type was around for quite a while before the alarm bells were rung, and could have spread, but because symptoms were mild no one knew to look for it. Everyone thought it was just cold, flu etc.
They think the L strain was a quick mutation, because it was transmitting from human to human. Hence why L transmits more easily, they do not have any evidence to suggest its more deadly. Just it’s the human version.
So there is a potential this was around a lot longer, as in weeks, before anyone knew there was a problem. It’s only now they know and the testing, that they are capturing it. In the weeks leading up to it being discovered doctors would likely think someone had pneumonia or something, if they got very ill.